"First Person" is a way of viewing an interaction with an environment,
"Puzzle" describes that interaction,
"Role Playing Game" is a description of various aspects of the game (generally outside the core game play experience),
And "Real Time Strategy" purports that a certain non-turn-based game has a high requirement for strategy.
These "genres" aren't contradictory...
"Portals" is a first person puzzle game,
"Fallout 3" is a first person roleplaying game,
"Deus ex" is pretty much a first person adventure game (and because an "adventure game" is more-or-less an alloy of "role playing game" and "puzzle game", it could be called a "first person role-playing puzzle game" or similar ugly phrase)
And unless your definition of RTS requires that the strategy be isolated from any dexterity tests, there have been a whole bunch of FPS-RTS mixes.
Further, you need to clarify what you mean by "remain top dog on the shelves". Hopefully, you don't mean to imply that most games sold are FPSs, because it's not really true: http://www.theesa.com/facts/pdfs/ESA_EF_2008.pdf (see page 5, 6) - at worst, FPSs are /among/ the most popular games.
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But, eh, predictions?
1) First person interaction isn't going away. It is an excellent way to get the player to identify with his avatar, as well as being a natural way of interacting with the world. The last point holds especially true with the current 2-stick hardware.
1.5) Top down "classic-style" RTS games aren't going to take off on consoles unless the hardware starts supporting keyboards and mice.
2) Plot elements (role playing) are likely to become more common and effective, for two reasons. Foremost, because they make good business sense: the number of people who like a plot outnumber those who hate plots, and secondly, due to rising production costs and instructive examples in story telling, it is becoming less expensive to add something which is more than an excuse.
3) Puzzle elements will retain their current position in the market - a powerful force among "casual" gamers, and a small part of many major productions.