I would like to be able to log in to two separate Sandboxes and do a comparison and deploy based on selected changes. This could potentially replace change sets in the lower environments.
Ex: I make changes in Welkin and via the UI in my developer sandbox. I'd like to promote those changes to QA. By having a comparison I know exactly what's available to either deploy directly, or at least get the diffs to be able to properly set up a change set - autogenerate a change set or unlocked package based on selection would be even better if at all possible.
For an example, please take a look at the SSDT database schema comparison tool in Visual Studio. It gives the options to deploy diffs directly, generate a script, or generate a DACPAC (package).