while it looks cool, I believe that this will only work well when the surface has been trimmed farther back than the extension that is being made, or if the surface has a straightforward topology and curvature. It looks to me like a combined untrim + offset on surface + trim. So basically you can already do this in rhino, but it will look less fancy. I am pretty sure that such interfaces require a lot of programming to get right. The question is, do you really need it to get the job done?
Same with the fin wish you posted: just a lot of fancy stuff, but not something you can model otherwise. I'd rather see new functionality being added like 5+ sided curvature continuous patches.