Billy + T3 + teleport is insanely powerful, it isn't an option to be allowed.
This was my gut reaction as well (shield + t3 + teleport also seems like it could be pretty beastly in some situations), but why not simply tune the cost of teleporting to make it not so?
I agree that special rules or exceptions are bad, but there's already precedent for adjusting teleport cost based on energy/mass cost of the unit (bp values TeleportMass/EngMod--could add in build time if you like). Include the cost of enhancements when calculating teleport cost* and you have many, many wheels to spin, all based on a central existing algorithm.
*Picking this out because it's an important possibility and I don't want to it get lost in the specifics here--mass cost of the telemazor (4000) is double that of the Cybran commander (2000). Just taking that into consideration--it isn't right now, TeleportMassMod is 0 for everything--could vary balance of teleporting with and without other enhancements significantly.
"But that's too complicated for players to learn"--there's a ton of shit (most of it, I'd say) that's too complicated for players to learn, and they approximate instead. Make the cost clear at the time and they'd do the same with teleporting.