They should just make an MMA HOF. I don't really care about the UFC HOF, because any HOF that doesn't count fights in Pride or any other short-lived major org is useless.
Something like this (must be 30 to be eligible):
Mirko Cro Cop
Georges St. Pierre
Only the best and brightest get in. Bones, Aldo, and Cruz are on pace to qualify. Guys like Belfort, Franklin and Machida are fringe cases. Shamrock, Severn, Sakuraba and Coleman type guys are just kind of before MMA was MMA and didn't have the impact Gracie did.
I would say a sport that's been around for 20 years you can establish clear top tens in HW and LHW divisions, top 5's in MW, LW and likely a top ten at WW, but that's merely because that division has been a gem of the sport.
HW - Fedor, Nog, CC, Mir, Couture, Frye, Severn, Coleman
LHW - Chuck, Shogun, Bas, Frank, Quinton, Wandy, Tito, Forrest
MW - Rich, Anderson, Dan, Sakuraba, Royce
WW - GSP, Hughes, Miletich, Sakurai, Fitch, Misaki, Koscheck
LW - BJ, Gomi, Florian, Edgar, Sherk
FW - Faber, Torres, Aldo
BW - Cruz
That's an average of two inductees a year since MMA began. Covers Pride, Pancrease, UFC Tournament's, Grand Prix's, and championships both earned and won.
The fighters on the fringes who should be up for debate are these types of fighters...
Igor Vovchanchyn, Jeremy Horn, Lyoto Machida, Vitor Belfort, Brock Lesnar, Tim Slyvia, Josh Barnett, Ken Shamrock, Frank Trigg, Diego Sanchez, Jens Pulver, Guy Mezger, Evan Tanner and Kevin Randleman.
Some of you may feel that only champions that have decade long runs should be in the Hall. I don't agree with that, I think a Hall of Fame should be about exposing fans to the sport and different eras/weight classes/styles. I would suggest any person that wants to seriously put Hall of Fame entrants into perspective visit this site.
In it you will see what sports do a good job with their Halls (NFL, NBA) and you will see what a huge joke the MLB Hall of Fame has become as most of the best and brightest of my lifetime have been kept out. You could make a Hall of Fame of guys not in the Hall of Fame thanks to the line of "only the best and brightest". Qouta's are the way to go