My vote would be the Vibrolux Reverb. A real AA964 circuit VR not the Custom Vibrolux Reverb of recent times. This could be a member of the current RI series, Twin Reverb, Deluxe Reverb, Super Reverb, or a custom shop hand wired amp. Personally I'd like to see it a standard RI not a handwired as more players would have access due to price. These are great club amps and the 2-10 speaker arrangement is not a readily available choice in the market.
I'd have to cast a second vote for Dual Showman or a Showman with switchable output impedence to use 4 or 8 ohm cabs. This comes mostly from my love for the surf guitar genre. There isn't much out there in the market place other than a Twin Reverb that will really do the surf thing at the volumes it was done back in the day. Clean, loud, glassy, tubeular.
What do you guys think? What amp would you like to see make a comeback as a Fender RI?