This is a great addition but I think it could be tweaked. I think it really needs to have the weight named, so ‘Former WBC Lightweight champion’ for example. If no space for both I would even remove the federation. It’s more important to show the weight than the federation imo.
For multiple weight champions I wouldn’t bother adding the weight or the federation. I would just have something like ‘Former 3 weight champion’ etc. (This for non current champs of course).