Here in Finland we have an indoor running track that the cycling clubs use for training in winter. Crr is heavy but it is fun for a couple of hours with a few of us.
Besides being safer than the roads, it could really help with bike handing skills like MTB/gravel. This might also work well in sandy soils like Florida or where ever one could get get a good pack and drainage.
Pretty excited about this for kids. I could see a parent putting their kids on a grass track where the parents can also see the kids riding.
Might even get a used track bike myself if there was one of these within a half hour. Hopefully we could get these every 60 miles across the country lol. Could be a good use of vacant land waiting to be developed.