I don't think RTS/FPS hybrids can work, after playing NS, Savage, and Battlezone 2. So far, all of these games have done really badly. NS is fun and all, but it only has about 150 American servers, and it's really not getting that much more popular.... I strongly doubt it will succeed on the retail shelves.
Probably the main problem all of these games have is that they give so much power to the players to completely screw over everything "strategical" about the game. Battlezone 2 was probably the only game capable of avoiding this problem, although only through MOD play. In stock play, players had very little computer opponents to deal with, so the players were immensely powerful and skewed the game. In MOD play, you could make the players just mere uber-soldiers on a battlefield full of dozens of tanks, and so they couldn't skew the game much. In NS, individual players can be so good that they can grab a relatively cheap unit or weapon and kill lots of enemies, making tactics and strategy next to meaningless. People say 3.0 will change all of this, but people have been saying this forever. I don't think the game can be fixed, the very core concept is what will keep the game broke (in most people's eyes), no matter what. Allegiance was a RTS/space-sim hybrid, it failed miserably too, again... forcing players to fill nearly *all* roles in the game, when AIs should have been involved everywhere.
Instead of RTS/FPS hybrids, I think it's time designers start looking at other genres to mix together. RTS and RPG would work better I think, as all players would be *forced* to work within a certain ruleset. RTS/actionRPG would work as well. RTS flight sims might be OK too, as flight combat is very smooth and organised, not fast-paced. It would also be easy to include enormous AI involvement, flight sims are very easy on bandwidth.
Another thing to consider.... I'd argue that RTS/FPS hybrids have almost no appeal to the vast majority of FPS gamers (counter-strike, rainbow six, Day of Defeat). I believe Savage, BZ2, and NS primarily appeal to gamers who are very fond of RPGs, MMORPGs, strategy games, etc (games that have no appeal to FPS gamers). I used to frequent the forums at www.pvpforums.com, when I realised that most of those people were seemingly obsessed with those kind of games, and also enjoyed NS. But few of them were DOD, Rainbow, or CS fans.
FPS gamers and RPG gamers are truly different breeds, and we shouldn't forget that. And while RTS games can appeal to both sides, I believe they most strongly appeal to RPG gamers. And so, if NS fails at market, you know why :-P