The stronghold mechanics maybe optional but if they have some references to a crafting chapter in the skills (about what resources you need when building weapons ...) so the the crafting chapter probably contain more than just stronghold. Then I don't think that that chapter will have anything to do with any magic artefacts. That will probably (hopefully) have its own chapter.
Of course the loot-table may contain resources, as well as currency and magical items. I just felt that I needed to point out that it seems highly unlikely that there will be loot specifically for building Strongholds since that loot would be wasted on groups who don't use the mechanic. There might be multi-purpose loot though that can be used for crafting in general as well as the construction of Strongholds.
Though for the construction of Strongholds I'd think it more logical to secure trade routes and natural resources like mines, quarries, farmlands and large swathes of forest than hunting for treasure in dungeons. But then again, I may be a bit too "realistic" about my fantasy role playing games =D