Good points. I want to address these two specifically.
A arena of 262s and B29s paying $25 a month each seems like it would be a good revenue stream.
Think of how many people would quit! LOL! I remember when they brought in the 163 and it was the plane the "Con" goers where allowed before anyone else could. That was back when we had good numbers and the MA emptied out very quickly. As it is now JG11 hunts my squad in 262 on our squad night and it just isnt fun dodging them all night. Id hate to see it more often.
I'm just being realistic about your family plan. I would need 4 accounts to play with my kids and $30 for 3 plus one for me would be $45 a month or close to $500 per year. I don't think many people would bite at that price when there's so many other FTP options. Even WoW has a FTP option and it was built on the subscriber model.
I think it would be very easy to police. All the accounts have to log on from the same IP. You have the master account plus the "family" Whatever IP the master account logs on from the other accounts need to log on from too. No Netfix problem with that.
There would have to locks so none of the "family" players could switch countries. On top of that it may even encourage more "Finetime" type players amd I dont think he could handle the competition to his "goatness"

I would love to see a FTP setup, and Id be happy if it was kept simple, 5 fighters, a bomber or two and a couple vehicles as well as the M3 and goon. No need to rotate plane sets. You want to try one of the others, subscribe. Also I think it would be easier to code that way, no need to make it harder to do. As for family, they could use the FTP plane set for those times they join in.
Again this is all on Hitech. How much effort does he want to put in, how much time does he have on his hands, and would it be worth it to him.