Do all modern FPS games require an XP system and unlockables in order to attract and maintain it's audience?

I'm talking mostly for the online part, especially exclusively multiplayer FPS games tend to do that a lot lately. Have FPS games really become slightly less engaging if they don't have constant progress tracking?

In other words, what does the future hold for upcoming FPS games?

We can see QL shifting towards this direction, that obviously means all potentially developed quakes will include this system.

Are such systems necessarily bad (e.g. QL Ranks)?