Rendering on the server was how Opera Mini worked (works?) for years. The low-end J2ME phones it ran on wouldn't be able to handle a full webpage even without today's JavaScript bloat.

Opera Mini was great on cheap Windows Mobile devices because your device didn't have the power to actually lay out a page, and the bandwidth savings on your slow cellular connection made the use of images make sense. Opera Mobile was preferable on Windows Mobile devices with better chips that could handle laying out a web page and had the bandwidth to work with embedded pictures that weren't tiny.