Judging from past history, ARs won't be banned. There will always be a work around. As someone else already mentioned, a stripped lower is a pretty cheap insurance policy if you wanted to go that route. A complete lower is less hassle if you don't feel the need to assemble something. 80% lowers with the new ATF guidelines are a total pain unless you're sitting staring at your own milling machine
, borrowing the use of your buddies is now technically illegal.
Ammo bans, remember AR15s typically shoot 5.56 or .223 Win ammo. These are common rounds in multiple firearms not exclusive to AR15s. It won't be banned. What MIGHT be banned or restricted is M855, which is the steel tip bullet. Frankly it sucked anyway for most people, but it was/is cheaper than M193 the all lead bullet. That's due to the military contracts buying so much M855 that companies have invested in the equipment to make those projectiles faster and cheaper.