I think dropping the even/odd scheme is a good idea.
Personally I'd go down to 2 active branches but then my group wouldn't be adversely affected by dropping the "old old stable" version since we invariably use the stable version. More weight should be given to the opinions of people who do use old stable versions. I would point out that the proposed change gives no firm guarantee on the supported lifetime of a branch at all. Could it be as short as two months? Potentially, since there would be nothing to stop us releasing a branch a month (unlikely, but from the user's perspective they would have no control over that)
Sent from Samsung tablet.