I like to use my filters for categories of senders, not just individual filters for every sender. It would be nice if we can click the "Filter" button and choose the option to append the selected email's sender or Subject etc. to an existing filter.

For example, I like to put all my emails related to airline points in the same folder. Having 5 filters for different airlines makes my filter list cumbersome to go through, so I combine them into one filter. If I have an existing filter that is already moving New Zealand Air emails to my Points folder, and I sign up with Qantas, then in order to add Qantas to the same filter, I currently have to manually copy the email address, open the settings, go to the filters' tab, find the filter, AND THEN finally I can click edit and paste the email address as an additional condition.

It'd be nice to not have to do that, especially if I'm doing an inbox organization project and have to repeat that process multiple times OR I have to create several filters and then deal with a secondary project of cleaning them up later.