Hmm.. I'm going to go ahead and say that, no, this is probably not something they should monetize. A large number of players are getting at least 670 gold keys per week, with more and more players opening thousands or tens of thousands during new kingdom releases due the the way drops work, and the chest interface has never caught up to support this. Paywalling what is becoming a necessary UI adjustment doesn't seem the right way to go here. I wouldn't want to see this as a low level VIP feature even, and I have VIP 7.
To put it another way, I'm willing to pay for extra convenience, but I won't put my money toward "not horribly inconvenient" which is how the chest system (and a couple other things, like leveling to a specific not-max level and ascension) are currently set up. Having a terrible RSI inducing interface and then paying for a slightly more convenient one, event just a dollar, sends the wrong message about the game and how they make their money as a whole. Not that I wouldn't pay, personally, I more than likely would, but I wouldn't be happy about it, and this is the kind of thing have been a dealbreaker for me had it been a part of the game when I was originally researching it. Also, as you pointed out, I don't ever want to open all my chests, but "enough" of them.
If/when the chest interface is updated for everyone, preferably with the ability to open a selectable amount of keys into the thousands at a time, I'll gladly show my support with an incidental purchase elsewhere.