New Concentration Rule

[Quartz]

Rather than change the Concentration mechanic directly, how about letting the PCs find a magic item that allows you to test the waters first?

Call it a Sword of Spell Relief, and it's purpose is to allow the wearer to be the subject of one Concentration spell without the caster needing to hold Concentration.

 

[Mon]

Looks like a decent house rule if you want to increase caster flexibility!

... One of the two spells you are concentrating on must be a spell cast on at least one other allied target other than yourself (but can include yourself if the spell includes multiple targets) ...

I'd change the wording of this part to:

One of the two spells you are concentrating on must be cast on willing targets only (possibly including yourself) or only catch such targets in the area of effect.

This way you can have a buff and an offensive/control spell up at the same time (or two buffs, if you're e.g. facing legendary foes and don't wanna burn slots on their auto-saves).