In theory, that's fine, but a total rewrite is the kind of project that can kill software.
If we only talk about Nim, the multiplicity of garbage collectors only materializes with version 1.4 [1].
Stability is not yet at the rendezvous with no less than 6 regressions [2] just in the last minor version and still 34 others behind [3].
Other compilers exploit the not new idea of transpiling to C / C ++ such as the ofront compiler for Oberon-2 [4]. Also I will not be in love with it without first looking for the disadvantages.
So in my opinion RenC does not need these theoretical advantages that one would seek in others but to finish the maturation of the ideas specific to its paradigms, its mutation towards autonomy, to stabilize itself and to offer a complete and independent documentation of the Rebol 2/3 ecosystem.
Why complete and independent documentation? Because to make the way to RenC, it is to go through Rebol2, then Rebol3, then the myriad of pages of this forum and other. This reminds us of the differences in behavior between the dialects, which is mission impossible for ordinary people with such exploded information. Then frequent changes because for the moment it is experimental.
In short, what I expect from RenC is to take stock of its maturation and to distinguish between what is good enough to constitute a first official version, what must be reserved for later versions, which still lacks essential, then actually deliver this first version with full documentation, an official site, ready-to-use binaries. If RenC always remains in this dependence on Rebol, in this state of research, without concretization, it will be able to have all the advantages of the Earth, but it will have no more practical utility than a philosophical reflection whose principles can advantageously guide action but accomplish nothing in themselves.
If this materializes I will find that I was right to choose RenC over Red, that it is possible for the weary traveler to make stops on the way to the top of the mountain where Carl's vision is located, instead of believing in the false promises of Red's Golden Calf.
PS: I stigmatize. To be taken with a grain of salt ...
[1] ORC - Vorsprung durch Algorithmen - Nim Blog
[2] Version 1.4.2 released - Nim Blog
[3] Issues · nim-lang/Nim · GitHub
[4] GitHub - jtempl/ofront: Oberon-2 to C translator