They've unlocked things with reckless abandon before (scrolls, ba hide, ba disengage) so I'm expecting some terrible unbalanced mess with caster multiclassing after their statement.
The worst would be allowing max spell level for all caster classes be determined by character level or highest caster level. But those would also be the simplest and I can't see them making the rules more complicated than 5e. Probably character level so players can't "ruin" their characters by going Cleric 6 / Wizard 6.
We will have Cleric 11 / Wizard 1 casting Disintegrate or something asinine like that. Single class casters rendered obsolete.
And why exactly does the game need this rule change when you can already respec at will?
