* On-boarding - new employees are no longer able to suss out the company by chatting to people they bump into. They need well-defined ways to meet other teams and to learn how to communicate and collaborate within the company.
* Socialising - there needs to be a regular opportunity (not mandatory) to meet up in person, even if there's no office.
* Communication - this is a biggie. The company can't just install Teams/Slack/Skype everywhere and expect collaboration to continue as before. Instant messaging apps are terrible for building asynchronous communication habits, since they incentivise quickfire messages. The company needs to publish guidelines on how to give status updates and ask for support, and potentially make communication skills be part of employee evaluation (if not already).
* Evaluation - remote work gives senior management a bad feeling because they don't feel like they know what's going on in the company. The root cause of this is that they're not actually evaluating employee output, but rather something else (e.g. how the employee contributes to meetings or responds to in-person questions). This kind of works in the office since those things correlate somewhat with employee quality. But remote work forces managers to think about how to objectively measure employee productivity solely on their work output... and some of them either resent the extra effort or just aren't imaginative enough.
None of this is to say that remote work isnt worth it. It absolutely is. But let's not pretend that it's a small jump from what most companies currently do.