I think it's a bad idea to go online-only. Flying people around the world is costly and can be exhausting, but there are a few benefits which are not provided by hangouts:
- hallway conversations which produce ideas. It's hard to manufacture these encounters in an online-only setting.
- social activities. Getting dinner and beer with the people you work with creates better working relationships.
I suspect there's a middle ground. Like having 3 online UDS meetups, and 1 in-person one per year.