Cross-browser AJAX is= a solved problem at this point. You can just go to Stack Overflow or find one of countless libraries to handle it to whatever degree of compatibility you want.

And all code is a moving target - nothing is future proof, especially where javascript is involved, but AJAX seems a lot more future proof than hacking image tags to do something other than loading images. It's baked into front-end templates and the caching strategies of the biggest sites on the web so it's not likely to go anywhere anytime soon.