I haven't ridden the boss since 2011, but I always felt the very front gave an incredible ride while everything behind the first row of seats was just a body-bashing nightmare.
How would millennium flyer trains work out? I would guess they'd need to be custom made to fit the boss, which would cost a lot, and would reduce seating capacity, but if an RMC makeover isn't in the future then the extra padding and articulation from flyer trains could work to make the boss more fun throughout the train.