Others have mentioned this to some extent, but what I've found the most challenging is when a company tries to do both local and remote, but was not remote-first. People who are remote are de-facto second-class citizens by virtue of the fact that they aren't included in hallway conversations or casual meetings. It's incredibly hard to overcome that. Teams that started remote-first are already well-practiced in inclusion and remote rapport-building, so it's less of an issue for them. But people who have the opportunity to meet locally and build rapport locally tend to get lazy and their remote muscles atrophy over time, unless they are making a very conscious effort, or the habits have already been deeply ingrained in them over time.

I'd add that this culture-setting rolls down from management -- if they aren't setting a good example, others will falter and the remote-supporting culture will fall apart.

Things like payroll, taxes, infrastructure are all solvable today, IMO, with the right resources or tools.