Lilith is making a base on Elbaph to help Kuma, so I can see Dragon arriving post-Elbaph. Plus the conflict with the trade routes could offer a decent time for Dragon to show off. Plus the Holy Knights have moved out so the Revos should as well. The issue isn't opportunity, it's more like Oda's really reserving Dragon for later and I hope we don't have to wait for the final war to see him in action.
Mihawk will show off if the Marines go after Cross Guild. The idea of Mihawk vs Sengoku is nice, but another instance where Oda may not actually bother with a relevant conflict for him on-panel.
It's crazy, both are incredibly strong and hyped, but don't get to do anything on-panel till later. I just hope Oda doesn't wait too long.