Considering I never had players actually counterspell (let along counterspelling a counterspell), it's still nothing I'm going to worry about.
And honestly... I'm just going to treat Reactions as I always have, which is not a part of a PC's "turn" but a separate window-- thereby not falling within the "two big spells a round" thing. Again... to me the whole point of the rules was merely just to stop power-gamer players from using their turns in the initiative order to spam massive attack spells to nova the enemy and thus making the non-caster characters superfluous. So me getting nitpicky about counterspells or other non-attack effects due to "the rules" is not worth my time worrying about.
You're lucky. We had groups where PC 1 would cast a spell, BG 1 would counterspell PC 1's spell, PC 1 would counterspell BG 1's counterspell, BG 2 would counterspell PC 1's counterspell, PC 2 would counterspell BG 2's counterspell. I wish I was exaggerating, we had 3 PCs that could counterspell and counterspell wars were common.