I think that kits are going to be more niched items that wouldn't fit into an actual pack (or they are things that "would have" gone into a pack and got pulled out of the pack because it didn't really fit, and because they've already paid for these assets they decided to just market them in a new way so they still reap some coin for the cost of having the asset made).
The other thing is, there are a lot of players who buy packs just for the CAS/BB items and not the featured game play (Vampires, Batuu, RoM, etc), so maybe this will be their way of giving players a choice of buying just "stuff" instead of the entire pack they're not really interested in.
It could also be a way for them to add more things players have asked for without having to create an entire pack around it
Instruments
Kids activities
Elder activities
Farm items (chicken coop, milking cow, etc)
It's also possible that it will end up being beneficial, maybe by taking out a bunch of objects from packs and selling them separately it will free them up to make the big packs beefier with more gameplay, since they can eliminate a lot of the "stuff".
Only time will tell.
I'm not 100% opposed to it because it's not mandatory to buy any of them.