Don’t see why the new system would mix it up all that much more than the system extant until last year. As it was, around half the people who applied to castle and Hatfield (for example) didn’t get places there so all those Hatfield-lovers would be randomly put elsewhere and applicants who really don’t want to go to Hatfield are now less likely to end up there as they have ability to name lots of other choices rather than being randomly allocated to any college, which might be Hatfield. In fact, that on that basis the Bailey vs Hill supposed split might become more polarised as people list lots of neighbouring colleges on their preferences, rather than being randomly allocated after they miss their first choice.
The new system is a much needed step towards reducing the number of students getting the catering style they don’t want, which is great.
Totally agree that avoiding shared rooms probably shapes some of Hatfield’s applicant group, as it so very share-y there (although my boarding school DS really didn’t want to share so would have been aiming to pollute the demographic of another college).
The major divide happened back when one applied to a college, not the university, but that is a long long time ago now.