Any accurate, reliable, multiple shot, and easily reloaded handgun isn't obsolete, strictly speaking, and as other posters have observed, its less the gear, and more the ability to use it.
Obsolescence means that all other factors being equal, there are better choices available than the obsolete choice, rather than there anything being inherently wrong with the obsolete choice. For example, I still have a 12 mHZ '286 with a 20 megabyte drive and a monochrome CRT that will run Word Perfect 5 perfectly well.
I just have better choices than that today, and choose accordingly.
Flipside, there isn't a heck of a lot of difference between Word 95 and Word 2007 to me, I hardly notice which one I'm using.
That being said, here's a list of handgun technology I consider to be reasonably obsolete for defensive purposes, and why:
Cap, blackpowder, and ball designs. They simply can't be reloaded mid fight.
Derringers, single & double shot. They don't reload quickly, handle poorly, and there are much lighter, higher capacity designs available now.
A list of oddball, marginal calibers, such as .25 acp, .32, etc.
Oddball designs like the Grendel. Come on, an autoloader without a magazine, obliging you to lock back the slide and press single rounds in through the top one at a time? Good grief! Another design I consider obsolete is the luger design. Apparently, for all their grace and beauty, they have reliability issues, and even the Nazis considered them obsolete in WWII. Ditto the broomhandle Mauser, given its size and weight.
There might be a few others, but I can't think of them at the moment.
As it stands, I don't forsee any revolutions in handgun design on the horizon.
There will be incremental improvements in materials and manufacturing technology, but the basic form factor and operating system variations have pretty much been worked out and elaborated, and the dead end technology paths have been largely culled off.