Unfortunatelly I can’t answer to that and assume the smaller track columns are simply locked for touch swipes, but as guy who is interested in the smaller Prime 2 and just can’t buy it (yet) due to lack of Serato Pro support at all, I want to give you my thoughts about what purpose I see in DJ Software support / implementation on AIO-units in general and why full screen functionality hasn’t to be of first priority:
Having the option to control Serato or VDJ via a Prime unit enables enhanced flexibility. It is the mere fact, that you can hook up your laptop with your software and use it like with any Denon or Pioneer controller before, while you also can work entirely standalone on the same unit without having to buy a second device, which makes external DJ software support so incredibly helpful and important. It is not about replicating the entire DJ software workflow and GUI onto the Prime’s screen. I wouldn’t care much about full touch support or hires-waveforms on the Prime screen at all, since that is what you have your laptop for in that moment (full size keyboard and 13"-15" screen, especially helpful during long wedding gigs with many music genres and requests like I face) and you can make full use of your 10" Prime 4 screen once switching back to standalone mode.
The fact that the Prime 2 and Go only have 7" screens that can only display 5-6 track columns at a time actually makes them more predestined for Serato/VDJ support than their bigger brother, since for situations where you really need more library GUI space (or lets say Serato Video control), the laptop can take the role for that, like before on regular controlers without on-board screens. Your Prime thus becomes a modular multifunctional Swiss Army Knife, which is already true for the Prime 4 and hopefully also the smaller silbings in future. Simply regard is as an bonus and handy add-on