I added the ability to use Tasker variables as parameters for Termux scripts. From my point of view, everything works as expected. The arguments are stored as a simple string and converted to a String Array when the plugin receives a fire intent. Quoted strings are kept together, while the arguments are splitted on spaces. This way you can just write the commands as you would in a shell.
Using Tasker variables works, though one has to type them manually in the configuration dialog.
It would be great if this could be part of the official app, since using an own build will interfere with the main apps package signature and thus would require to also build Termux. This way you can't benefit from PlayStore updates to the official main app.