CapnZapp
Legend
Actually, I would say the issue isn't with Concentration per se, but with levels.Don't change the concentration mechanic. Change the spells that require concentration.
While you still don't know level 9 spells (and maybe level 8), Concentration works fine as written with no changes necessary.
But as you begin to master magic, the 5E limitations start to chafe. They make it impossible to have truly impressive high level mages.
So what I would like to see is an official (optional, but first party) codification of the various relaxations of the magic limitations that we already can witness in the form of top level NPC casters! [emoji846]