Animaker
I don't really agree that these coins somehow violate the "theme" of the pool. OHM is a unique asset class which there is a clearly large demand to borrow against and adding additional stablecoins to the pool gives OHM lenders more assets to borrow + lets them tune their risk portfolio with more granularity than just USDC vs DAI risk. It's not like throwing a bunch of random tokens in the pool that would simply leech off the existing liquidity, as there is very little demand for borrowing stablecoins against other stables (the only non stable in the pool is OHM which has borrowing disabled).
Adding these assets is delta positive in basically all cases imo, as even if one of these stablecoins were to collapse, OHM lenders would not be hurt (they would actually benefit as they could repay their debt for an enormous discount), and adding these new stablecoin projects in the pool will attract more liquidity for OHM lenders.
Some of these projects (FEI and FRAX especially) have even publicly committed to using their treasuries to bootstrap Fuse pools with their token(s), which could lead to lower borrow rates as direct treasury deposits give the pool a minimum amount of capital that is agonistic to the rates they're earning (as these projects simply want to gather more adoption for their token).
I think this proposal is awesome and love to see Fuse pools being used to scope out future partnerships and push the frontiers of DeFi lending! Adding these assets adds basically no risk to the pool as the only users would would be affected by their collapse are the lenders of the experimental stables themselves.
If you wanted to be extra cautious you could set their collateral factors to 0% to ensure there's no possible way for a collapse to damage other lenders (though I don't really see this as necessary as the only assets able to be borrowed are other stables anyway).