After selecting tiles with b, I'd like to able to right click and get an option to send the selected tiles to the same location in another layer.

I had some of the same ideas as a few others here about a way to indicate what tiles are for what purpose/placement and thus be able to 'paint' a level in or have a level be generated. I highly doubt anyone would want to program that, though.

A fill function would be very, very nice.

It would be neat to make hotkeys that will change the field of view to another area of the level.

Warnings for possible crashes/errors.

Better copy/cut/paste stuff, especially for events.

And many of the other excellent suggestions in this thread.