Should we add Shardminds as a race in the world?
I think they'd fit in perfectly, though that should be obvious.
If so, should they be playable or unplayable?
I'm on the fence about this.
If unplayable, how common should they be, and will they be hostile to players?
I think shardminds should be fairly rare but otherwise act like normal sentients, i.e. some should be hostile, some beneficent, and most fairly neutral, pursuing their own goals.
Should we change their backstory so that they were created by the mages of the past?
I'd like to think of them as arising naturally from magical energies with the Warforged as an imitation.
If they are unplayable, should they be able to speak to players?
Yes, though as I said above they should be uncommon.
Should we add the Warforged as a race in the world?
Same as above.
If so, should they be playable or unplayable?
Again, on the fence. I'm personally a fan of having all races in the world that aren't blatantly OP or Always Chaotic Evil be available to players, but I don't know what others think. Ask Hukuna.
If unplayable, how common should they be, and will they be hostile to players?
They should be rare, but not as rare as shardminds. If there was a reason in the history for them to be mass-produced, they should be more in the "somewhat uncommon" area, like elves in many high-fantasy settings. (i.e. large numbers that often make contact with other races, but still unusual.) They'd probably be more likely to be hostiles than shardminds due to the fact that they are soldiers (though you might change that with their gloss in this story, idk) by nature, but still be mostly like other humanoids.
Should we change their backstory so that they were created by the artificers of the past?
I think so.
If they are unplayable, should they be able to speak to players?
Of course.