Depending on the route Ian can be hanging out more with Holly, continue his ways with Alison, have his date with Gillian or deal with Louise's expectations about her new status. Maybe check on Wade if you got a poor outcome for him and he's MIA. There's quite a few things for him to do. There's also Cindy, Emma, Cherry... heck, most of the cast is available for him to interact with in the meantime.
Yes, there is a lot Ian can be doing. But nothing set up like it was for Lena. Also, it was easy to isolate Lena and Axel for their scene as Axel is the only LI that would already have prior knowledge of Lena's family situation and where to find her. Besides, most of the rest of her LIs tend to disappear for long stretches as is, especially now that Mike is ghosting her. Ian will not be isolated and will have the full cast to do something with. It would make cutting to Ian's POV more complicated, because how do you decide which girl, or Wade, to hang out with? So does EK create a scene for each girl and then bloat the development time and put the rest of Billy's trip on hiatus? Or does EK skip that and try and isolate Ian similar to Lena's POV during the Beach House chapter?
I feel like Ian's POV, if the plan is to make the primary focus of this chapter Billy's event, has to be something somewhat islolated. Perhaps Gillian's meet up, training at the gym, or searching for a house are all things he can do without needing a crazy amount of work on EK's part creating a bunch of different scenes. Don't know how, or even if, EK sneaks a lewd scene into any of those scenarios.
Edit: Just want to clarify, IF the plan is to make Billy's event the focus of chapter 14 in a similar fashion to the Beach House in 12; then I think Ian's POV needs to have some limitations. If this is going to be business as usual then Ian's POV can be whatever.