A Jiujitsu friend of mine recently told me he heard that Randy Couture said in an interview that he believed submissions will play less and less of a rule in MMA as fighters become more comfortable with them, and eventually most fights will be decided by standup and wrestling.
Recent UFCs sometimes seem to confirm this - there are UFCs where almost every fight is a knockout or TKO, but I can't think of one where almost every fight ended by submission. Yushin Okami's failure to get Rich Franklin to tap to a kimura that was tight and extended quite far also make you wonder whether more and more fighters will be able to just muscle out of them.
For my part, I just can't imagine submissions dissappearing from the game. First of all, learning to defend submissions properly requires years of jiujitsu training and practicing submissions. And I can't see why any fighter would spend years learning them and then not employ them in a fight.
The recent season of the Ultimate Fighter actually had no knockouts (some TKOs), but many submissions, and while they almost never end the majority of the fights, most UFCs have at least one or two submissions.
What I believe is changing is true is that most fighters entering the UFC today do not see themselves as submission guys, having been trained primarly in wrestling or in boxing. There's also the fact that crowds today like to see the knockout - there's not much clamoring for submissions against knowledgeable fans.
And let's not forget (let's not forget!) that both fighters having good standup can lead to a stalemate as well. Boxing and K1 both have many fights that go to decision, and in boxing that means up to 12 or 15 rounds without a KO.
What is true is that fewer and fewer fighters can expect to just impose their specialty on their opponent, whether than specialty is wrestling, standup, or submissions - fighters are just too well rounded. Submissions seem to have lost their edge when jiujitsu fighters are stall by wrestlers with good standup or kickboxers with a sprawl like crocop. But this is only natural - if you have an advantage in one area and the ability to determine where the fight takes place, you're going to win. Stand up fighters neglected their ground abilities early in the sport's history (and wrestlers their standup and submission skills), but these days it is often the jiujitsu man who fails to enlarge his skill set.