you mean like the framebuffer gets wholly rerendered when something within the content chenges? like an animation or text input into a form? this is of course an angument, but then as you see there is none who can implement your frontend on 68k.
That's what makes scrolling or anything dozen times slower than it should be...
When i started OWB porting, i had a try at the SDL backend of OWB for fun, and it was absolutely terrible (on PPC), since it was also rendering the whole buffer for any damaged area.
Even if you keep SDL, you should at least do it properly and modify it to only updated damaged areas, that would really increase performance.
Apart from this, i think you really overestimate the work to do to adapt it to MUI or Reaction (they already exist! And the Reaction version is recent and more optimized). So just go for it, one step at a time.
