I do think Jimmy should be in the Ring, but just for grins let's play devils advocate for a bit, shall we?
Looking at the players in the Ring of Honor, how many of them were on the team just a few years? The vast majority of them played for Dallas for 10 years or more. Charles Haley was on the team for 4 years only, but he was put on because if he wasn't, he would have beaten Jerry to a pulp (JUST KIDDING!) But Haley made an immediate impact, from 11-5 to a SB win his first year.
Only Landry and Schram and Brandt was non-players are in, and all were with the team for 29-30 years, oversaw the team from start to America's Team, many conference title games and league championship games.
Jimmy was only with Dallas for 5 years. And it's easy to say "his" team won another one, but the simple fact is he had been gone for 2 years before Dallas' last SB win, several key players left in that 2 years, the assistant coaches had a lot to do with the SB XXX win imho.
Jimmy won 2 SBs, same as Landry, but Landry went to 3 more, and the 1975 team got there largely due to Landry's coaching, with 12, count 'em, 12 rookies on the team just getting there was one heck of an accomplishment, losing to the Steelers, who won 4 SBs in 6 years meant they were an extremely good team, no shame in losing by 4 pts to them.
Just noting that there could be a case made that Jimmy doesn't deserve to be in the Ring, vs. others there.
And I would also note I'm not saying this is my view, just thought I'd throw out some thoughts. It IS the off-season, ya know!