Even at a wider, multi-group level, we are able to address issues of innovation and serendipity by creating time and space for them. One of the best tricks is encouraging lots of small presentations on non-work or semi-work topics followed by lots of open ended conversation. People show up by mutual interest outside of their project based work and talk. I run a book club roughly themed to application development and every session I meet new people from across the org and exchange ideas. Some of these contacts have resulted in valuable insights for later projects. Volunteer projects and hackathons can serve a similar purpose.
These are just examples and we are hardly perfect, but I if the projections of an massive increase in WFH bear out at all, you'll see culture adapt to it as well- people will get better at socializing on screen, feel more free to ping with questions, and will find these alternate avenues to collaborate. I'm less confident that society outside of work will adapt as well, but I wouldn't be surprised at all to see a long term increase in young people continue to live with extended family or social clubs.