Hey,
I've been following this thread, and don't particularly want to pipe up, because more than likely I'm wrong...but has anyone considered the bridge?
My thoughts on getting low action (as someone who has set up their fair share of guitars) is that 99.999999999% of the trouble ends up coming from the bridge. Sure, you can radius the frets perfectly, and have the truss rod perfectly set, but without the proper settings on the bridge and nut, you just can't go as low as you'd want to.
My problem always comes from the saddle height settings which are THE most neglected settings on a bridge. If the bridge is not properly curved, you're just not going to get the ultra low action and playability you want. On a flat fretboard, you don't have to worry about that, as it's easy to set all the saddles to be perfectly straight and level, and set the nut to be just like that. On a guitar with a floyd for example: without too much work, you can make all the saddle heights perfectly even, but have fun doing any real radius without a crapload of shims... Basically, the way I understood it, this was the whole reasoning behind having a compound radius fretboard. By making the fretboard have a flat radius near the end, you can compensate for having less adjustment on the bridge, and the nut holds the strings at the proper radius at the other end.
Either way, the point is that in an ideal situation, you can make any guitar play with ultra low action, and bend fairly well. If you want to have ultra low action, like the feel of a classical guitar and want to bend madly...then maybe the flat fretboard is for you. The way I see it, with a 1/4 inch fretboard, even if you did radius it, you'd still slot the thing for frets first. So as mentioned before, just cut the fret slots and fret it as is when building. If you don't like it, just pull out the frets, radius it (just remove the nut and mask the headstock), and put the frets back in.
Peace.