This is my own rules because I always hate the idea of "classes" putting players inside of a box and restricting everyone else. Consider it the possibility of cross classing or whatever.

You may purchase the Talents of any other Profession but each rank has it's base cost increased by 2 experience points. You may not purchase the Talents of another Profession during character creation.

So if as a Fighter I wished to purchase some Druid powers and be a kind of nature "paladin" I could purchase the first rank of Path of Healing for 5 XP if I had a teacher (including spending the quarter of a day practicing and making the roll) or 15 without a teacher. Rank 2 would cost 8/24 and Rank 3 11/33

It allows players to diversify even more without taking away the advantages of your chosen profession. You simply loose out on efficiency of xp expenditure to branch out in those ways.

The only problem with this is the ability to powerplay super hard. Also, a druid can still hit very hard with a high stat in strength and melee. If he takes any of the general weapon talents, Fast Footwork and defender he is a veeeery good fighter still. Add Lucky, Melee Charge and Executioner - you now have a druid killing machine.

I agree with pellejones to an extent. The general talents provide enough diversity to add a combat or survival spin to any character without really having a need for multi-classing, but there are no magic talents. So if the Rogue or Minstrel your rolled wants to dabble in magic, it's simply not possible. One option to fix that would be to add a "Magic Initiate" talent that allows you to learn a rank 1 spell from any discipline. If you already know all the rank 1 spells for a discipline, you can then move on to the rank 2 spells and so on. Additionally, you would not automatically get access to the General spells discipline. 

That being said, I am going to experiment with letting my players purchase talents from other professions. Initially I am going to keep the XP cost a lot higher though, kind of taking inspiration from the "Learning Magic" section on PHB pg 116. You may purchase a talent from another profession at a cost of 9X the rank AND you must have a teacher.

(Edited to 9X the rank, not 9X the cost)

This would create a world where professions are not important. +2 XP to buy a Profession talent from another Profession isn't that much. All the players would be just "adventurer" and nothing else. 

Mutant Year Zero has a talent (Jack of all Trades) that allows you to change role. This means that in MY0 you are allowed to have two roles. You can only do this once though since you can only take a talent once so there is some planning here for the player and also when since you can only increase specialist skill levels and specialist talents for your "active" role. This approach is probably much better if you want to include "multi-classing" in FbL.

I dont think professions SHOULD be important.

If anyone is familiar with the ffg sw games they did it well and similarly. You get talent trees for free based on "class" but anyone can buy into any other classes talent trees for a cost.

People dont fit neatly into a box defined by their job and characters shouldnt either. We are supposed to be roleplaying people inhabiting a world, not a class selection from a video game. What one man can learn another man can learn as well. They may not be inclined towards it. But that doesnt mean incapable.

The costs could be higher then my initial proposal. But they shouldn't be so expensive as to be restrictive. There is already alot to spend exp on and death is right around the corner. These power builds will die just as fastbefore they ever get made.

... There is already alot to spend exp on and death is right around the corner. These power builds will die just as fastbefore they ever get made.

Some GMs (such as myself) let the players in the group create new characters with the same amount of experience that their lost characters had accumulated.

The reason I wouldn't apply a rule like this to my campaign is that I think most games that use professions/classes are intentionally designed around not letting individual characters be too self-sufficient. Because of that, the players' focus should usually shift towards building a strong party rather than characters that don't really need each other for anything.

Additionally, many of these games' pre-built challenges explore this very facet - so if a GM relies heavily on this sort of material, some effort on re-balancing challenges would be required.

But if this is something you and your group are looking for, then absolutely! In that case, I would just recommend making the cost of "multiclassing" higher than what you've originally proposed, for balance reasons. Or you could maybe port the Forbidden Lands setting into a skill-based system such as Genesys (FFG) or one of the BRP-based games - Mythras and RuneQuest are great options.

... There is already alot to spend exp on and death is right around the corner. These power builds will die just as fastbefore they ever get made.

Some GMs (such as myself) let the players in the group create new characters with the same amount of experience that their lost characters had accumulated.

The reason I wouldn't apply a rule like this to my campaign is that I think most games that use professions/classes are intentionally designed around not letting individual characters be too self-sufficient. Because of that, the players' focus should usually shift towards building a strong party rather than characters that don't really need each other for anything.

Additionally, many of these games' pre-built challenges explore this very facet - so if a GM relies heavily on this sort of material, some effort on re-balancing challenges would be required.

But if this is something you and your group are looking for, then absolutely! In that case, I would just recommend making the cost of "multiclassing" higher than what you've originally proposed, for balance reasons. Or you could maybe port the Forbidden Lands setting into a skill-based system such as Genesys (FFG) or one of the BRP-based games - Mythras and RuneQuest are great options.

Sure, the cost could potentially use some adjustments. Maybe cost it like skills? Rank x5.

Either way. It balances out because someone who does not invest in the talents of other professions will have more skills (and thus more dice to throw) or more talents from their own profession/general talents. Someone who invests in other class talents spend more to get less.

Additionally, the general talents already let everyone get some kind of perk in everything. It's just that the more interesting talents are in the profession ones. Nobody is going to be the best at everything because the increased cost is going to be prohibitive.

One option to fix that would be to add a "Magic Initiate" talent that allows you to learn a rank 1 spell from any discipline. If you already know all the rank 1 spells for a discipline, you can then move on to the rank 2 spells and so on. Additionally, you would not automatically get access to the General spells discipline. 

How about: Magic Initiate treats the Rank as one lower for spells you can cast, mishaps, and safe casting.in other words:
Rank 1: rank 1 spells auto mishap
Rank 2: rank 2 spells auto mishap, rank 1 spells roll for mishap
Rank 3: rank 3 spells auto mishap, rank 2 roll for mishap, rank 1 safe cast