Classic CAN vs CAN-FD
Sadly, this problem does not have a clear-cut solution. The lack of a large selection of affordable MCUs with CAN-FD capability (especially more than 1 CAN-FD controller) paired with the current silicon shortage is likely to drag adoption out for the next few years at least. The biggest issue is that a single node that is not FD-compatible causes problems for the entire network. A band-aid solution to this might be to implement conversion nodes as @tridge mentioned, to connect a classic network to an FD one. This is far from ideal, I know, but it might accelerate adoption a bit. If anyone has any good ideas on how to go about this, please speak up 