Pop cap is necessary for a couple of reasons, most common is to limit performance issues of those with lower end machines.
If you want the perfect solution to the pop cap, Take the pop cap system from BFME 1 and mix it with the system used in HW2;
Battle for Middle Earth - Pop caps were small because the lag issues were horrendous BUT, say you had a pop cap of 80 and you was in a 4 player team game, your ally dropped leaving you to face twice the numbers. Well, the pop cap would double for you, effectively giving you your allies pop cap on top of yours, this gives you a far better chance if you want to continue the game.
Homeworld 2 - there was a pop cap in place but you had the option to increase it if you knew the people playing your game had machines that could handle it. If you had it at standard then you were limited to pop caps for each type of unit. So you could build battlecruisers but only a max of 3 at any given time or 14 interceptor squads or 21 frigates... you get the idea.
Mix those two and you will have a far superior pop cap system also allowing for more fleet variation (online skirmish anyway)