rescue bots?

Everything you have said in this post is assuming we have experimentals and that the tier system is based off of the supcom system. Please check your facts

Why pull in enemy units? They will only shoot things and make pain. Friendly units will fly into the facility and get all the mommy love they need.

You're trying to solve a problem that could easily be fixed by proper scouting and army composition. If you don't want to lose a bunch of units then scout the enemy defenses and build an army that can take those defenses down. If it's point defenses, then use artillery. If its artillery, then use fast raiders.
This "rescue" mechanic might sound like fun until the enemy is doing it too. If you're about to destroy and enemy army, but at the last second they get rescued out of the blue, I'm sure you'd be more than a little frustrated.

So no, I don't want this in the game.

ok i see how its viewed as a bad idea but i think it would be pretty cool to see

Ever since the original RTS game dune 2 by westwood studios this has been done. And it was immensely cool. However i've thought about it over the day and the more i think the less it seems to easily fit into the game (or more accurately doesn't add anything).

even if it was designed to just automatically pick up wounded units, transport them to the back of the battle (we are assuming magical level unit AI here), repairing them to return to the front. Given the lifespan of the average unit is less than a terran marine in the brood wars manual, the things would just have nothing to do.

I'd rather see the return of the necro, which is kind of the same but more useful. or if you wanted to be more awesome, giant pondering spider litches which wander the carcase strewn battlefield returning the dead to life to continue their endless cycle of destruction.

or if you wanted to emulate the function better, a combat engineer with 8 low power nano-lathes that auto target your damaged units (so it targets 8 things).

You could also reclaim the wreckage and build a new bot. It's almost like not giving a crap whether they live or die.

A machine like the Necro in TA would be better, no?