Is it possible to play a channel solo in the VSE, through a shortcut or python? I mean like ex. hide/mute all unselected channels?
You can solo a track/channel by choosing anything other than 0 in the preview window.
A track higher shows...
You cannot render out this way however. Also there's an issue with alpha, you can still see below the strips with a crop or other kind of Alpha over enabled. See the cropped image below, you can see the track beneath it.
However if you select all of the strips in that channel and group them together using Ctrl-G key, then the new Metastrip is produced with no alpha over enabled.
No way to natively hide/mute channels. Only strips:
'H' & 'Alt+H' will mute/hide & unmute/unhide a strip.
'Shift+H & 'Shift + Alt + H" the same, but inverts selection.
However, this add-on can mute/hide entire channels: https://github.com/venomgfx/addonitos/blob/master/space_sequencer_channel_tools.py