I think that could work over a small area. I can see accessibility
problems in "wiping it off with a rag after a few minutes", when I'll
have just varnished an entire hall; though I suppose your method
avoids the need to maintain a wet edge, and therefore to do the whole
floor at once.

The "few minutes" can be less, it's just that it's easier to apply with
a brush than a rag.

Point taken on the thickness of the film. Possibly one coat of the
water-borne would be enough to seal the wood for colour; before
completing with high VOC.

The overall "colour" is partly determined by the final coat, so you
might create a kind of yellow glaze effect. I'd be a bit worried that
the high VOC wouldn't wear well on top of the softer water based film.

I'm probably trying to be too scientific about this. I've now hoovered
the floor and tack-ragged it with white spirit. Once that's dried I'll
apply the first coat of watery Ronseal then take it from there. My gut
feeling is two coats of Ronseal, de-nib, then two or three coats of
the matt solvent stuff.

The rag method doesn't really need de-nibbing, that's one of the
benefits. FWIW I've never been able to get the same result with
brushing, however thin or diluted the coat.