There won't be a hub as such, just the ability to go back and fourth between levels, so stats need to carry across if when going back into an area/s already visited. Not sure if RtCW allows for this.
The main reason for using Unity (or other) system would be access to per-pixel unified lighting system, the trouble with RtCW and idTech3 in general, in that models are lit in different ways depending on their use, a problem that's compounded should they contain alpha, and are used within a fog volume. Per-pixel is supposed to alienate these issues (not tested to check yet though).
That's the problem, using RtCW means being able to make something quickly but it can't be monetised. Using Unity et al means a long development time but the end result could be monetised (unfortunately it just gets to a point where it becomes untenable to continue providing these excruciatingly time hungry projects for free). Going the former route obviously means using pre-existing assets (which limits some of the things that can be done), going the latter route means making everything from scratch (Copyright infringement isn't necessarily avoided doing what you suggest although 'derivatives' would be fine in the sense that an influence could be seen).