1. as there is a ctrl+enter to split subtitles, there should be a shortcut to join one subtitle with the next (or the previous) one.
2. every ctrl+z should show where the undo(s) was/were done, in case of a wrong/double press of the keys. same with ctrl+y.
3. in many cases there are too many unnecessary gaps between subtitles. there should be some option to stick together several/all subtitles.
4. there should be an option to move ALL subtitles n milliseconds back or forth.
5. there should be a search and a search+replace feature through all the subtitles.
Thank you for your suggestions, Adam. I liked them and marked your post accordingly.
Re the 4th, though: see "Shift subs forward" and "Shift subs backward" in the Timing Tools (clock icon) tutorial: you can specify the amount of time in hours, minutes, seconds and milliseconds.
Your other suggestions would be very useful!
Thank you for this useful observation, Andreas. Also, the action should be reversible: maybe the person who deleted the gaps would notice that the result is worse? And a former subtitler might object too.