I finally caved last year when my 2003 Dual G4 stopped being able to play YouTube videos and bought a MacBook; with enough time and effort you can strip the latest OSX down to run fairly normally. I don't think they'll ever lock into an iOS-type environment; the default will move more and more that way but there's still a very large market of "creative professionals" that want the "classic" OS X experience (not the Classic experience that I dearly wish were still around...on a tangent, if you hunt around a bit you can find Rhapsody for Intel Developer Preview VMWare machines - how I wish that UI had stuck around!); not to mention the fairly newly entrenched base of geeks and programmers who fell in love with the middle-era releases for the super-slickness of XCode combined with the familiarity and strength of Unix. I can see them going so far as to hack up any locked-down releases; there's a small and sporadic project to tweak the kernel code so one can install Rosetta on the new versions; I'd expect and hope for more effort if needed.
If worse comes to it I'll just install older versions on newer hardware - their build quality is still superior to just about anything else out there, the higher cost is far offset by the longer useful lifespan.