I'm not convinced Counterspell is a fun spell to begin with. I mean..instead of two casters doing something, both do nothing with those spell slots, and slots just get drained. Spell Mantle vs. Dispel Magic is a much more fun active mage vs mage thing.
From experience, Counterspell resolves in extremes. Being absolutely epic or a mis-used spell slot. It'll definitely be the most problematic reaction to implement.
