I know from experince how hard it can be to balance a game but I don't think a few hard to find ysalimari creatures would make much difference in the game and it would add a new element to the game that is easily controlled simply by changing the number of them in game. That and it would be just cool to watch those force users cry for their moms when there power vanishes.
1. There are currently no creatures implemented in the game.
2. The list of the rules pages is old work, and while it is likely they will make it into the game, it is unlikely they will all be the initial release, or that they will be the entirety of the creatures that are ever implemented.
3. The intent for creatures is to have them spawn somewhat randomly. If the number of ysalamiri were to be controlled and regulated, they would require an additional mechanism specific to them.
4. Ysalamiri provide a programming challenge, not only for their abilities, but also for the specialised equipment required to sustain them outside of their natural environment, and the fact that their power increases the more of them that you mass together. When you consider the fraction of the population this work may be relevant to, it is hard to justify the work required compared to the effects.
5. This also appears to be more of a suggestion than a question.
"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."