More distinction between regular tracks, the master and sends. I’d prefer a configurable color myself. Something that works at first glance, both in pattern editor and mixer, and also track scopes(!).
allow sends to be moved next to regular tracks, so you can group stuff that belongs together.
(3. make the master movable… why not?)
The master splits ordinary tracks from send-tracks so that you can use just one shortcut to create either a normal track or a send track.
A color might give a good indication which track is what, but a distinct place will cause less confusion as send-tracks have specific limitations.
Yeah, okay. But wouldn’t it be nice to be able to answer “there is a command to create a track and a command to create a send track, so you can create sends where you actually are using them”? 
Huh? 
A distinct place will cause less confusion than colors? The default place wouldn’t be touched at all, the restriction wouldn’t need to be touched at all (it would still be “you can only send to the right”), so how would that be more confusing? If a user moves a track, why should they be confused by the new location of it???
Also: once you used the program for, say, a month, NOT being able to group the sends logically is not only confusing, but also annoying. But I guess by then you’re out of the target demographic.
Which shortcuts would you like to assign to these then?
Ctrl+s for instance is already for save song.
Confusing in the sense of you want to record notes and accidentally your cursor sits in a send-track.
Or you are adding commands in a send-track that were actually meant for a note-track to the left of it.
Or users that want to apply FX to incoming audio in the sample editor but the sendtracks are not in the list.
That may not a problem at the beginning but it will be annoying when these things start to happen to you frequently. Trust me, colors will turn ordinary when working with it often that you will unawarely make such mistakes very easily.
Ofcourse, when sendtracks are allowed to be moved everywhere, this will become a problem of the user.
i think we are looking for color codes here. 
EDIT:that way you could color code the tracks and the sends used for that track to the same color,that would give a good overview of what belongs together IMHO
I haven’t thought about that since I can’t even run Renoise on the laptop I’m currently on, but that can’t be so hard…
That is no different than entering notes in the wrong note-track. If you don’t look where you’re clicking/typing you will get confused, movable sends or not…
I don’t really get what you’re trying to say here, and I can’t open Renoise to have a look.
Umh, sorry, no. “Trust me”: I know myself better than you do 