Yes this would be great. Not only would you then have a weapon to kill people in aircrafts (which you now don't, meaning a person can avoid being killed as long as he's mid-air), including the dogfights which are really fun, but we would finally be able to use an aircraft which isn't slow and can land almost anywhere.
Making it unlock at level 100 would make it safe, so people won't randomly shoot anyone and even if they do they can be punished, and since it takes a while to get to lvl100 those players are regulars players so it actually will hurt them.
Other than shooting, rustler is the only aircraft that's fast and has the ability to land/take off in almost every road. This means it has potential to be used in missions, any kind of long-distance delivery really, and also there was talk about unique air-delivery missions coming in future, so this would fit perfectly. This isn't just a thing that destroys vehicles, there's more to it.. Just casually flying around, doing stunts or flying through tunnels is something people do, and you can't have the same result nor satisfaction with the slow ass dodo or helicopter. Not to mention it takes a while to get good at it, so not everybody will use it. I don't think any nerfing is required, since it's only lethal once you figure out how to properly use it..just like any other weapon.
The only issue with this, is what would dmers do with it. Hunting cops is -for whatever reason- allowed so this would mean you could just fly around the city and destroy everyone's vehicle. This is a problem, yes, HOWEVER, don't pretend this isn't a problem right now. If you want to fix it, fix it by changing the rules, not by limiting us of any extra features because some people like dming. Considering there aren't any decent pilots around from what i've seen, although rarely anyone plays a solo cop anyway so even if there were any i wouldn't notice it, this wouldn't be an issue at all. If this is the only reason why you wouldn't want to add it, again, start by fixing the gameplay and the rules because the pointless DM right now wouldn't be any different than the pointless DM with rustlers.