I think Ryan Gordon (aka 'icculus') is proof that the right solo person can do such a port :-) Nevermind Casey Muratori or others I could name...
There are many small, talented indie developers that definitely have the right set of skills to bring an engine to a new platform, or to one that's just slightly different.
For example, porting an engine from Linux to FreeBSD or some other UNIX should be trivial, but impossible without source code access.
Now I doubt many games are going to be ported to those platforms, but imagine a 3D walkthrough program for an architectural client or manufacturing facilities where UNIX is still found.
There are many small, talented indie developers that definitely have the right set of skills to bring an engine to a new platform, or to one that's just slightly different.
For example, porting an engine from Linux to FreeBSD or some other UNIX should be trivial, but impossible without source code access.
Now I doubt many games are going to be ported to those platforms, but imagine a 3D walkthrough program for an architectural client or manufacturing facilities where UNIX is still found.