Termies could be a permanent character thing without breaking the game. Think of every other rpg out there. not everyone wants to be a barbarian. just make it different and have limitations like ower (not slooow) or long respawn. and require higher levels or series of achievements to unlock it. Similarly, termies could be a squad/strikeforce unlock...but also permanent
Heck. It WOULD be in lore for them to move slowly. They were designed to clear spaceships and boarding actions. So anyone fast enough could just get around them and attack. Also, they would make tasty targets for assault squads and vehicles/devastators.
Problem is in urban warfare how do you stop a thousand terminators? A thousand terminators on your own side is the only thing that springs to mind, not to mention seeing a thousand terminators would just ruin the atmosphere of the game for me.
Perhaps limit them? It would be following lore procedure and there already is going to be certain classes/ranks that are held by one person.
How about your own dreadnoughts, terminators, and devastators for which you will presumably have in the same ratios. This is why reconnaissance and communication is important
Missing the key point. No warhammer 40k fan wants to see a thousand Terminators. It's so fucking dumb.
I'm so amused by these conversations when the tabletop game itself ignores balance restrictions, every match can potentially have two Special Characters with tons of terminators fighting Imperial Guard with Sisters of Battle, which is hard to see happening a bit in fluff. Or even see hundreds of marines with rare dreadnoughts fighting off a bunch of cultists lead by a Dark Apostle. The tabletop itself ignores fluff for gameplay.
Personally, I think Terminator armor should be insanely rare, to the point that only the members of the War Council and Strike Force leaders (that is, the guys who lead 100 other guys) should have it. In return, people in Terminator armor should in fact be living tanks (with their own weakness against anti-tank weapons, fittingly). Consider them THE end-game reward for players. Of course, the same should hold true for Ork Mega-Armor, Chaos Terminator Armor and some sort of Eldar equivalent (Seer Armor/ Exarch armor?)