Something that has been kind of on my mind is the relationship between JavaScript's undefined and Ren-C's NOTHING state.
I've set it up so that if you have a JS-NATIVE that doesn't have a return statement, that returns NOTHING. That's consistent with plain functions that don't have a return statement.
However, it seems to me that reb.Value("print {Hello}"); should not return undefined the way that reb.Value("select [a 10 b 20] 'c"); returns null. One reason is because JavaScript is bad about conflating falsey things, and it considers undefined to be falsey. Whereas Ren-C considers nothing to be truthy.
Guess my point is that it seems like an area where noticing the parallel is useful, but care should be taken in where to make the mapping apply...