as much as i love idea of rolling plane set, it was tried in practice in WB and it did kill the game. First 2 weeks of the month when early war was being played - there was nobody in the arena.
The timeline was changed for 2 days before RTP and map stays, if I remember, 2 weeks. IMHO biggest reason for players to disappear were hacks and then consequences when hackers were driven out.
I would recommend different approach - make a map that is divided in 3 separate sections, with 100000ft mountains between them to keep "transfers" out. Early war planes in one section, mid second late last. Put some strategic targets in each, so that if you want to whack radar factory, you just have to pick up He 111 
Not sure if that would work, but maybe worth a try ?
That might work. Just wonder how many point greedy überkitepinger will demote themselves to fly something under 400mph, but for my kind of easy kill it sounds good. AIs which are present in match arena are just too hard nuts at least for my skills.
free to play planes to be lambs for a slaughter sounds like a bad idea for all involved.
- new players get their heads bashed in before they can learn anything and even if they do learn/know something - are hopelessly outclassed by vets in superior rides
- old players are degraded to "club the seal" game and i don't know about you, but killing newbies ( even in late war planes ) is no challenge/fun for myself.
As being in receiving end, it's not fun either. Kills motivation when pinged down in almost every flight before getting anything done.
secondly, i don't think 15$ a month is a such a huge barrier. To play sims people spend thousands on desktop/VR hardware/GPU. For sim enthusiasts, 15$ a month likely isn't a challenge. I would say that currently it is outdated graphics that are simply pushing people away.
I doubt if it pushes old players away, but may really make new ones to go after some eye candy. For me, AH graphics are just fine. Especially after WB they are superb.
