I'm not sure that protocol changes prevent mass adoption. If Mastercard change somehow its protocol it doens't prevent the user from using it
One of the problems that Mastercard never had/will have is introducing gambling codes like SPV into the protocol. Imagine being known as Mastercard, "card for the gamblers"
Yes, you are talking about code changes, that's fine, for optimization, bug fixing. The other word is "protocol changes" these would radically change the incentives of the coin.