The geometry of a 93 frame is pretty much incompatible with running 100-120mm forks, but that's what the new Prestige is designed for. So I'd guess an RC31 would be too short and you really need to be looking at least at an RC39C, if not an RC40.
I think that would be a really great bike - but it wouldn't be an updated retro in style, but a completely contemporary bike with a high handlebar, much like a Cotic.
I tried a 100mm travel bike the other day, and it is my opinion that I neither ride hard or fast enough to warrant such a device. As you say, to buy a modern bike and build it up to ride how I like my bikes to ride is a silly thing to do. Hence I shall be building a modern twist on an older frame as my daily.
Somerset, like 'Heartbeat' with newer cars!
Retro MTB: 1992 Cannondale 3.0 Deore XT M730. 1992 Marin Pine Mountain Deore DX M650.
Retro road: 1992 Eddy Merckx Corsa Extra Telekom Shimano 600 STI. 1993 Dyna Tech Ti.
Modern: 2006 Wilier scandium Ultegra 6600. 2014 Wilier GTR Ultegra 6800.