A lot of firearms enthusiasts aren't old enough to remember the slow start Glock had when it was first being imported into the US. Some firearms instructors may have been at it long enough to remember some experiences from the late 80's. (Anybody else have a copy of the FBI report from their FTU about Semiautomatic Pistols dated from 1987-1988?) Glock had their own teething problems in the early years. Glock also failed the DHS testing several years ago, too.
Anyway, the market is Glock's to lose, so to speak, much as it was S&W's to lose when the M39/59's seemed to dominate the LE field when revolvers were being phased out as service weapons.
I suspect we'll continue to see Glock losing market share as the other manufacturers are recognizing, embracing and responding to the civilian LE market's apparent desire for plastic-framed service weapons.
I suspect the newest S&W, Sig & Beretta plastic service pistol designs will start to accelerate the erosion of Glock's position.
Springfield may finally get some momentum going in the civilian LE field, too. They aren't exactly aggressive in this regard, for whatever reason.
HK would do better if they didn't hold their point so high. Sometimes it all comes down to bid/costs.
Some of the other larger companies seem to be focusing on the commercial market instead of the LE/Gov market, at least for the time being (Taurus, Ruger & FN, for example).
Walther seems to have its attention directed toward LE/Gov customers located outside the US, although their 99 series is a good one worthy of attention. Who knows what they have in mind?
These things seem to ebb & flow in cycles, you know.
I wouldn't look for a clear cut "winner" when it comes to future dominance, but more of an ordering of the various big names as the plastic pistol concept continues to make itself known.
Now, if the US military ever shifts away from the metal-framed Beretta, then we might see some scrambling ... (although I'd think we'd see the mainstay of the combat small arms addressed first, meaning the rifle/carbine inventory, which is as it should be considering how long the M16/M4 has been in our inventory). I wouldn't hold my breath for any movement for general military sidearm changes any time soon.
An announcement for new DHS and FBI submissions & testing might stir things up again, too.