Possibly the final evolution, I'm tempted to try an additional arb too- although this isn't really necessary if you've got the ability to tune spring rates.
Would this make the Stage 3 subframe more friendly to those who haven't got coilovers/method of adjusting spring tensions - i.e. standard spring/shock kits (e.g. H&R cup)?
Indeed it would, but if you're looking for something to suit a road suspension set-up then I'd reccomend the Stage 2 frame which retains the ARB, you don't have the caster adjustability a stage 3 gives though.
We've got a few more things in the pipeline first, but if the market demands it, then we can supply