It is already possible to set a specific assignee for a via-email-created issue with the "CC Assignee"-flag. (CreateOrCommentHandler)

This is not really intuitive for the user, as the CC field is also used to add watchers to the issue.

It would be better to use the first "To"-Email found (of course only emails different to the catch-email-address).
In case there is more than 1 additional "To"-email-address, these user(s) should become watcher(s) too.

Usage example:
To:

{catchemail}

,

{Assignee}

,

{Watcher1}

,

{Watcher2}

CC:

{Watcher3}

,

{Watcher4}

...