1. has some legs, as rarer versions of units were concepted before, honestly.
2. can't be fully correct, as even if you ignore the mockup having multiple woman (female knight/warrior), we'd have literally 0 units without goblins and some breeding fodder.
3. Upgrade sources might be more likely.
Notice that we have a mockup of gold, which implies costs for building things are returning. Raids and conquering areas might give a small trickle or a lumpsum of material/gold, unless we get alternate means, like selling women monsters to fund a Black Market.
There is a good chance that conquering an area with said chess piece might capture some of said units. We might not ever be able to capture female units counter-raiding us anymore, and instead rely on them only being rewards. Perhaps completed raid areas can be raided again to capture units. Perhaps harder raid locations give better trait rewards/rarer units in the future.
From the
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that also stated 'Chest Sizes being Fixed', mentions thoughts on how wave mechanics could implement bosses and abilities unique to rare and higher units (this implies sisters are just rare versions of woman). And the breeding mechanics for Shortstack in another image.