Vacation timeshare properties are already an R2 per 310.3, so shouldn't we all be approving them as R2? Is the conflict in the "transient" designation. and the fact that they are not "timeshare" and are more of the VRBO/AirBB type of transient? It looks like code assigns "timeshare" with the idea that the occupants are somewhat familiar because they stay longer, return often and have an ownership stake, making them more akin to an apartment than a hotel room. Whereas a VRBO/AirBB would not.
This conflict has taken other forms, such homes designed and built to the IRC but used as transient rental lodging. To me the big issue is the lack of familiarity with a transient population, which can hinder egress. Typically not a concern in small structures, but can be an issue in large ones. If memory serves this was an issue in NC due to some very large coastal rentals and at least one fatal fire. A lot of those buildings are three stories, with as many as 8 to 10 bedrooms. Fill up a house like that with 15 or 20 people, unfamiliar with the building and egress, add in some booze, and I can see a potential problem. But I'm not sure the same level of concern would exist between an IBC R2 and use as an R1 because they ae already pretty close as far as restrictions.