Any response to this would be speculation.
I would think rifles configured in a certain manner would be banned if a ban were put in place. Might include flash hiders, bayonet lugs, adjustable stocks, high capacity magazines, etc. The lower is the serialized portion of the firearm. Your lower means you legally already have an firearm, it's just not functional. I don't see how barrels, stripped uppers, BCGs, LPKs, etc would be banned as they are simply parts and the lower is the firearm but there would certainly be a rush on those parts if there was a ban in the works which would make them very hard to get. Certain parts aren't easy to find in stock as it is.
I'd proceed as normal with putting together your AR. If you really thought there was going to be a ban you'd already have a bunch of parts.