It could be nice to have all email communication just on email tab (by option), but there should be possibility to get notification about state that new emails that have came and it is available on email tab and way how to set to be fired transition options like auto-reopen issue or change a state (e.g. from Pending to In progress) and possibly function for JQL resently commented by email.
With the exception of adding an entry to the email log instead of a comment for existing issues, execution of transitions, setting issue fields from email content is already possible.
Setting a field from email content could result in adding the issue to a queue. Or the transition that is executed by the mail handler could have a post function that sets a field moving the issue a queue.
If you talking about common Jira post-funtion it is not possible set default Component/-s field.
Frankly speaking such field initialization should support also static set of field to value without matching with any regexp against to email.
A field rule may match anything, e.g. regex .* on sender email address matches all emails, then you can initialize the fields as you wish.
So expected case:
if there in no issue match create a issue if there is match create just email log entry (on email tab on particular issue)
if it is created new issue then assign issue to particular component otherwise add component if it is not already in, but no replace so just extra component.
if it is not created new issue give change to state or fire event such way that can be processed by Jira on issue type level e.g. as this could be done for comments https://confluence.atlassian.com/display/JIRAKB/HowTo%3A+Reopen+an+issue+when+a+User+comments
In general to use it as it is now, but every email communication will be primarily on email tab.
Maybe alternative could be that JETI create comment like that:
... issue was commented by email: <<link to email>> ...
So clicking on link will switch you to email tab and such email log entry (possibly hover and show it in popup window).