Ahh, Frontier, I still remember I read about it in old press of the times, it was considered a "miracle",
but I never got my hands on that, I had a too weak machine then
would have loved played it at the time.
Anyway - yeah, Frontier modeling style would be definitely doable,
(it is already, with "custom shapes" and "shared center of rotations", although extremely awkward)
a modeling tool easing that job could be done and be useful.
Also, if you don't use textures, you don't get in the "keep ratios" issue of non-perspective texture scaling,
and you can theorically go whatever odd proportions/sizes you want.
As for Mario, I *think* we are already getting to a high polycount,
if you consider you'd have to add many more polygons for the environment,
but if you only go with a single character and not much more, it could probably do...
Well, we'll see, it would be interesting making some experiments on some limited modeling
and implementing some "grouping" function for moving "parts",
but I don't know if/when...