The Sims 4 Business and Hobbies Apartments on top of Shops

I believe they will be different features. These new small businesses seems to be possible on a new lot category, Small Business Venue. The For Rent units had their own lot category (Residential Rental?). I do not expect them to get merged, as hey are the selling point of twoi different packs, but also because the system of For Rent was quite bugged for many, so implemening it with a new pack would probably be rather risky...

The B&H apartments is not really a thing. The mechanisme is there only to separate your household's domain from the public domain (store), in oder to avoid customers and employees occupying your private rooms. I think you can have just one household on the lot, not multiple rental units.

There is more info on simscommunity.info. It says you can run businesses from your home lot. However, it doesn't specify if residential rentals are included in venue types.