You won't know until you read the bill and even then only after the law is passed. BUT, some of the things I've seen flying around, (and they are some ridiculous proposals, ban M1 Carbines?) they are bans on new sales and NO turn-in/repossessions. I very much doubt they would even address half-built AR being assembled by the owner. Of course, if they ban the sale of parts, then you could be in trouble. BUT, despite the red hearing argument the anti-gun crowd uses for AWB, that they have to dry up the parts supply, they never ban the sale of parts, which still goes on after the ban.
As well, you have to check the law and interpretations of the authorities that would enforce it, its usually interpreted that once you've purchased and registered the lower receiver, stripped or otherwise, that is the same as purchasing the whole rifle. So if you got your stripped lower before the ban, your should be safe. Honestly, who is ever going to know if you finished assembling the rifle before or after the ban? Of course, if they ban the sale of specific parts, like a flash suppressors and you don't have one yet, then your out of luck, but still in compliance with the law.
Business's will of course stop assembling rifles on the date the ban takes effect, because they can't sell them. That is what they are usually concerned with, I doubt they will go to the trouble of adding language to prevent private owners with all the parts already from assembling a personal rifle for private use.
We won't know yet, but only if they add to the current proposals that all assembly of rifles must stop on such and such date, only then should you have a problem. Even then, only if you purchase parts after the deadline that have a record of the sale, would anyone even know that you completed the assembly after the ban date.
Set you priority for parts purchases on the thing most likely to be banned. Hi-capacity magazines, Flash Suppressors, Barrels with muzzle threads, collapsible stocks, bayonet lugs, pistol grips, etc. Even then, they may only ban those features on new rifles, the sale of parts can continue just as long as you don't put those parts on a Post Ban purchased rifle. And don't think some states won't have cops at ranges asking to look at your rifle and registration paper work to see if you've added ban features on post ban rifles.
BTW, the definition of an Assault Weapon is a weapon with a selector that allows the a full automatic mode of fire, something already controlled and new manufacturer banned under the machine gun laws. Every RIFLE or PISTOL on the Assault Weapon Ban List are NOT ASSAULT WEAPONS, by definition. But, that is a typical tactic of the left, change the language to fool the people.
Likely this time, the law will have a provision that the Attorney General can update the list of banned weapons, and the current attorney general is likely to make sure that anything resembling a "Black Rifle" is going on the list as soon as it appears, so there may be NO MORE POST BAN RIFLES.
I just had a thought for a protest, Pictures of BLACK RIFLES with the Slogan BLACK IS BEAUTIFUL, we can send that to the attorney general. :lol please do NOT get over sensitive on race, I think that is a clever slogan.