I have three formerly 26" disc frame mountain bikes converted to 650B. The first one, a Ibis Mojo Ti from the late 90s that I sent off to be converted to IS disc mount. Tested out a 650b wheel set with 650 x 47 tires which fit comfortably. Then a 650b converted a steel Breezer frame that's also a 26er from 2011 or 2012 that I got for cheap. And lastly, I sent off another Ibis 26er aluminum frame recently to get repainted and while I was at it, added IS disc mounts to the frame. They all work well for commuting, light mountain biking or gravel/bikepacking rigs. No need to discard an older 26er frame for being "outdated"/