I know I've mentioned this before, but Vauxhall tried that as a test during the Supertouring era.
They had the Cavalier 4x4 which allowed them to run a RWD version as well as the normal FWD. The RWD was slower. The transmission losses are far too high.
BUT it must be said, John Cleland had nothing but praise for it in a recent article saying even done the way it was (4wd converted to 2wd) it drove so much better and was more balanced, having had more development time he thought it would be better
As far as the idea i thinkyou were thinking of, buying a Q4 and emoving front shafts making it rwd, i did similar recently with my scenic RX4 which i was plannning to rob the runnning gear from for my superchared RS project...
but it didnt work
basically because its too electronically controlled like i think the Q4 system is and i had to convince it to carry on sending the power there rather than the 70-80% maximum
best way i can put it is it was like having your mum in with you, you booting it and your mum screaming in your ear to slow down before youve started getting anywhere (the mum being the ecu
As far as full on rwd conversion.. thats the way im looking at now but its far more complex in the simpler easier areas than people look at,
Tunnel is easy
Rear floor pan diff mount it easy
Front leg engine mounts is relatively simple to manufacture
BUT the engine would in mine sit 1/3rd through where bulkhead now is so id need complete new front subframe design as half the rear frame load bearing points would now be compromised
Hardest part.. steering as the engine would be through the rack if left where it was
so complete remanufacture there, many options but alot narower than needed
Then the undeniable fact that if i was to go to all the effort the current lump wouldnt make it worth it so id need build a forged lump for an honest reliable 240bhp-250bhp