Microchip's webpages say it's "Not Recommended for new designs", but I see it deeply stocked at multiple distributors and there's nothing on the distributor sites about "Not Recommended for new designs". The MCP2518 is significantly more complex, more so that we need for this application, and we have significant experience with the MCP2515. We'd prefer to stick with the latter if it's going to stay in production for a while.

Almost every device Microchip have ever made is still available.
You can keep using that device, but you may find it becomes more expensive than the newer device.