We have an unlimited unit cap in LOUD - and while in one perspective that's nice to have, it's not a practical limit. Even on the best of days - with a very streamlined codebase like LOUD, on the fastest of machines, the practical upper limit, before you start seeing unit count induced side-effects, like severe UI lag, and SIM degradation - is about 5 thousand units - in total. We do, on rare instances, see games with 10k or more, but those are rare indeed - and usually involve 1 v 1 situations.
I hear what you say about unit cap being given the same kind of real estate, on the UI, as the other two resources - and I offer a suggestion here, that we've had in LOUD for several years now, unit cap growth.
It is possible to turn unit cap into another resource, one that can be managed by the player, or offered up as a reward for things like achieving veteran status. For example, in LOUD, we have various structural enhancements that will lower the unit cap cost of certain things like T2 and T3 Pgens, T3 shields, etc - giving the player the option to 'invest' in more unit cap with his resource base. Also, each level of veterancy grants additional unit cap, encouraging a certain kind of gameplay that's less wasteful - and it's permanent (unlike the structural enhancements). And lastly, that poor servant of the ACU - the SACU, gains additional value as a total replacement for your horde of lower level engineers by actually lowering your unit cap usage.
Long and short - it's possible to make some changes that make unit cap a flexible part of the 'Supreme Commander' experience and still have some kind of lid on potential performance issues.
