Hey, if you can make it work consistently in this RP, I cannot begin to object; I'm all for it. Though I don't agree that change in the attributes of the setting is necessary to keep things exciting (or less predictable), there is no reason it cannot happen.
As for Mindfray evolving into a physical effect, it sounds like a completely and entirely different power. Yes, it could be developed by a user who has mastered Mindfray (letting the physical manifestations of their mental projections become weapons rather than flaws), but as soon as it becomes physical, how is it a Mindfray? I know it's a discussion of semantics and in practice it is redundant, but it has its own classification, closer to the descriptor of Psi Lance - "The ability to manifest pure psychokinetic energy and fire it as a projectile. Extremely draining, and must be strengthened over time." (BTW: Really gotta make
that info more findable)
Mind control is temporary, but if you infect an enemy and it pops a Chryssalid that makes a permanent ally. In fact, it makes you a permanent ally for the number of remaining enemies on the field. Come to think of it, I don't know how the game engine treats Chryssalids vs aliens (including other Chryssalids), I don't play MP. They don't pop Chryssalids out of Mutons, right? So maybe they just didn't like how the Chryssalids' gameplay works vs other aliens, not wanting to make the way that works in MP canon.