Textastic 4.1 for Mac adds the new keyboard shortcuts “Toggle Comment” (Cmd-/) and “Toggle Block Comment” (Cmd-Option-/).

Actually, this is already possible using the app Secure ShellFish which allows you to access SSH/SFTP servers as folders in the Files app. You can add those folders as external folders to Textastic and open and edit the files as if they were local.

Can you please send me a short video that shows the problem? I don't see this problem on my devices.

To show the scope at the cursor location, you can use the keyboard shortcut Ctrl-Shift-P (this can be changed in Textastic's settings -> Keyboard Shortcuts -> Code Editor -> Show Scope).

Here is the sublime syntax file used by Textastic:

JavaScript.sublime-syntax

It should work if you put the file "Ink.tmLanguage" from the "grammars" folder into the following location in Textastic: 

Local Files/#Textastic/Ink/Ink.tmLanguage

You can open two windows of Textastic and put them side-by-side. There is no diff view that shows you added and deleted lines though.

Would it be enough if this could be specified in the SSH connection's settings or do you need this to be on a per-tab level?

Looks good, but I think there is a semicolon (";") missing at the end of the "@charset" line in local.css. 

Textastic only adds a row above the standard iOS keyboard. To make this available in all apps, I would need to provide the full keyboard. It's not possible to just add a row like I can in my own app. This means I would need to re-implement the standard iOS keyboard, which I don't think is feasible.