Yes I can see that would work, and I will probably try to use a variant of it in the short term.
There are a few of problems with it from our circumstances.
We are trying to integrate this with an existing system, and the structure of that makes this problematic. We run a software as a service system for hundreds of customers, varying all the time. Some come, some go. We are trying to give them all their own mailing list capability, but automated as far as possible so they don't need to think too much (they aren't that computer literate).
First off, each of our customers have their own directory, and in there are their assets (header images, logo's, footers etc., all specific to their branding). The assets are all named the same (header.png, footer.png etc. etc). What I really need to do is just figure out the folder name. I could do that from part of the address, or part of the mailing list name etc. (for example we would mandate the mailing list names insisting they contained the folder name in some way). Then using a bit of twig code twig we could easily construct the URL for the asset we want.
Second problem with using just Mailwizz tags is we would have to create all those assets with the name [LIST_UID].png and stick them in a common directory and that would be an ongoing requirement. We also wouldn't know what the name would be until we had actually created the lists. If the customer had multiple lists we would need multiple .pngs, even though we want the same image all the time.
Having twig enabled would allow us (I think) to solve all these neatly. Can I ask why you don't like twig enabled in this area? Is it a support issue? I haven't looked at the code but I think it would be reasonably easy to implement to feed the data through twig (after your tags are resolved). Maybe on the screen that enables twig you could have some text saying that as twig is a third party offering you cannot offer support for twig related issues? I think having twig in the these circumstances would open up all sorts of possibilities and make mailwizz more powerful.
Oh, and just as a final thing. When you use the [LIST_NAME] tag, you don't really get the list name, you get the list display name. I'm thinking if I could use twig then I could encode my folder name in the actual list name (with some unique data after a - maybe, so the list names are unique) and then I could have as the display name a more human readable name like "CUSTOMER LIST" or something rather than "CUSTOMER LIST-foldername" which is a little ugly.
Hope that helps,
Colin