PS: Remember SPORE? They did something similar, take a look at that.
SPORE is not as bad as people often make out. Yes i did die inside once ihad played but that was because of my expectations above anything else. Each"level" or section of the game was relatively good, especially theinitial two levels, but they were all very basic. In the end it was obviouslyaimed at a much younger audience, which yes is rather stupid for such a"complex" genre, and several people who were around 10 at the time ofits release loved it to bits. There are things to be learnt from SPORE but ithink that’s mostly from a marketing point of view in my opinion.
Anyway before i go on to much about SPORE I'll to back to the originaltopic.
Would there be a market for it? Yes probably, CO-OP gaming is becoming morepopular and this fits snugly into that, the wide range of appeal could be agreat selling point as well.
Would it be expensive? Yes to be done properly anyway. Chances are you wouldneed to create your own engine and unlike other games you will have to makeseveral very good games instead of just one. This could mean, if you have fourgenres in a game, you will have to have four games that could stand uprelatively well on their own.
Is it possible? Yes i would think so but as i kind of said before it’s justa case of time and money. You would also need some very talented programmers etc.for it to work smoothly.
Would i play it? Personally i have always wanted to design/play a game likethis so yes i almost certainly would, if it was done well of course.
As for my general thoughts on the game you described i would have to agreewith most of the other posters. It’s very complex the nature of it would meanyou would be inevitably tempted to add more elements to the game which wouldalmost certainly ruin it in the end. This sort of project would require you tobe very very strict with what you do and how you do it, even more than youwould have to be when you design a "normal" game. If i was you iwould at least attempt to design you own standalone game for each of the genresyou intent to use instead of jumping in at the deep end as it were. You couldplan to do what CCP are doing with EvE and DUST "random number i never remember"i.e. make one game that’s a space based MMOG then later create another, in thiscase an FPS, that has some form of indirect effect on the MMOG and visa-versa.There even issues with that but it may work a lot better in the end than an allin one game.
In terms of game-play there would need to be several tweaks from what youhave said. In the RTS sections i would be tempted not to make them classicRTSs, I’m thinking mainly about the ground one, but to make them almostRainbow6 or even the Savage series style of games. One of the FPS players is a"commander" and can call in certain support/create buildings/giveorders but the whole time there’s very much on the ground and part of theaction not just sitting over-viewing the battle. The other elements would, inmy opinion, need to be largely independent from each other in a sense. Havingan amateur city builder or in fact not having one at all at the current timewould not penalise a 4X player to much and make the game impossible for the 4Xplayer. Also what would happen if it took a few weeks to build a perfect cityonly to have it destroyed a day later by another faction? There’s a reason theSim City doesn't have another player storming your city with troops at random.
The more i think about it the more i think it is doable but also the overreliance on a guild like system and thus limit the appeal of such a game to adegree. It may work better as a single player but that would probably requirecutting back in areas.