Usually new vehicles are placed on newer edit, for two reasons:One way to incentivize new maps is by introducing new vehicles. People may want to check out the new "flying kraken/mino," whatever it is. The interest may only last a short while tho. But at least it gets a few maps into rotation. But please don't incentivize by removing maps that people love. That's old-fashioned book-burning Nazism, LOL
1. As you pointed out to get folks to play new maps/edits
2. I don't want to break/destroy "classic" maps, so careful introduction of newer vehicles on older maps is required. Notable exception was flying saucers on RedPlanet.
Nearly all of the "Classic" maps I leave unchanged except to update vehicles with updated/fixed versions (eg. FireTanks, etc.)
Back to the topic, I don't see much need to change the rotation.... IMO its a split decision, anything shorter invites too much repetition. Even now, last week we played serveral maps (eg. Nevermore) EVERY NIGHT, so no need to shorten the rotation...if anything it made me want to make it longer.
Most new maps take several edits to get right (usually anywhere from 3-8 updates), this is because no amount of thinking/bot testing replaces human players... some of the edits work out, some don't.. But often people complain (the flyers are too powerful, while a Troop Carrier sits unused; The Classic Mino is too weak (lolz) because they want to not really aim, etc.) once we start playing them a bit more the tweaks get better, like things like Bionyx for example which is pretty fun. I think Dry Ice has gotten there too.