Most popular sizes afaik are 17mm and 20mm - fitting many 18650 and 21700 hosts respectively. Even something like the Texas Avenger “TA30 – 30mm series : Same as 22mm only larger silk screen basically. You can sand it down to anything between ~22mm and 30mm.” (from here) would add extra versatility.
At that point, a shared oshpark PCB and a parts list (bonus points for links to mouser/digikey/whatever) would get it into a few people’s hands (I’d try my hand at a few personally).
Beyond that, if you can get mtn electronics to sell them, that would be amazing.