The percentage of maxed TH10's has some relevance, but it's not that critical to the introduction of TH11.
i had been hoping that TH11 would happen soon but with TH10 defences getting a regular double upgrade over the past few updates it's hard to imagine that TH11 is close. They could have simply turned the past few updates into a TH11, thrown in L12 walls, +20 Hero Levels, a few troop upgrades, another Dark Troop and spell and call it a day.
I don't think every TH10 maxed or nearly maxed would rush unto upgrade to TH11 if there will be. You know why? They would now have penalty against TH10 especially TH9... Beside, if TH11 offers new or add defenses and walls think about the existing size of our village.....But I'm not saying its impossible everything is possible for SuperCell if they want.