+1 - it is really needed for my team to be able to update the order of the tickets in the Epics. I think this should be prioritised by the Atlassian team - here are my 2 cents about it:
The purpose of the roadmap is to plan ahead/forecast/visualise the backlog/progress of the team. It is also used to keep the backlog up-to-date and be prioritising it accordingly. The backlogs are being prioritised mainly on priority/effort which is something that will be great to be visualised in an easy way.
Moreover - the order of the tickets in the Epic can be updated only from the Roadmap as this functionality is disabled in the Epic view - therefore, it should be possible to see the priority as well.
P.S. Adding the screenshot from @Christoferson Chua as it didn't visualise there.

Can't believe this is not a standard setting. Heavy +1 here