I would love to see snapshots of current activity (sp_whoisactive) taken on a regular cadence (e.g. every 5 minutes would be very useful for troubleshooting).
So in the current activity tab I can select a snapshot time from a dropdown of taken snapshot times. Backwards/Forward buttons advancing to the next/previous snapshot would very powerful.

Having the top queries and waits etc. is super useful, but being able to see a snapshot of the active running queries around an incident would add a lot of value.

Appreciate that is potentially generating a significant volume of data so appropriate retention/default capture options/server configuration/snapshot frequency would be required.