Perfectly prepared to line myself up in the cross hairs in search of enlightenment, so here goes.
C of G considerations aside, whats the problem with simply strapping on some nice neat 'n tidy, tried 'n tested turbofans a la Dornier 328 instead? Even if they can get the present powerplants to eventually behave, theres a lot to be said for greater commonality. And C-17 demonstrates that FOD ingestion isnt an issue.
However, it does seem mad to close the C-17 production line when it plus C-130J is surely more than sufficient trucking capability for most moderate air forces. And I imagine C-17 would be a fair bet for a tactical tanker too.
Yeah I know, politics.....but go on then, shoot.