I think it depends. If they are also required to allow 3rd party stores, and one of the third parties has a “buy” button while the others have “lease (lifetime)” buttons, it might sway a decent number of people.

Same thing with consoles, if one has “buy” and the other “lease”, then it might not convert everyone but could it take 5% of sales? 10%? 20%??

I don't think the general public is engaged enough to understand the difference between "license" and "buy". They will look at the button and think "This is what I click to get it" and don't understand that they are just temporarily renting the thing. To most people, "license" is a noun: something you carry in your pocket to drive. The word is already overused by media vendors to confuse people.

It does defuse any excuses like "why do you say I can't buy games? I bought this game just now" and that can be a stepping stone to actual change.

That's assuming there's an alternative.

Yes, the language should be clear and precise.

Also, if the whole industry string-replaces "lease" for "buy," I doubt the effect will be much.

The point is to not mislead people. When you write "buy," you are implying that the "buy"er is obtaining a perpetual right to use the software, subject to certain rules (i.e. you can't make copies and redistribute it). "Buy" implies the buyer has an absolute right. When "buy" actually means a temporary revocable license is issued, and the buyer has no rights, that's a problem.

It should in a functioning system, people who see lease or license on a game may be more hesitant to buy it and might pick a game who differentiates itself by marketing itself as being a permanent purchase.

You are being downvoted but your reasoning is absolutely correct. We nerds on the nerdy techie HN love to believe that people will act correctly if they are properly informed but people have repeatedly demonstrated that they don't care. This kind of regulation that only targets wording and nothing tangible will likely just blend into the background noise of 1000 other legally mandated notices in the fine print that people skip over. No surprise this is already a law in California which is littered with useless prop 65 warnings.

I expect many people would accept clicking "license" instead but it's unfair to assume that people don't value ownership as such or that they won't in the future. It's fair to ensure that people are made fully aware of what they're paying for in a clear way which doesn't conflate it with other forms of possession.