Umm, do we really need this? You apear to be taking markup flexibility out of templates and hiding it where themers are not going to be able to access it.

Unless there are sound performance and/or security reasons for this change, I would suggest sticking with what we already have. It works perfectly well.

One thing you have to understand is that of you want to encourage theming, it has to be flexible and comprehensible. Most themers do not find a sources files comprehensible, and from their perspective it certainly is not flexible. TBH, without spending a couple of hours studying it and asking a lot of questions, I can't even tell what all the ramifications of this PR are.

Can you explain the advantages?

As an aside note. Please see https://github.com/elkarte/Elkarte/wiki/Make-a-new-theme, hands-on tutorial for a new themer. I started up the page, but it's just a stub I'm afraid. Please correct it and add to it. What is there to know, where to look, how to change basic things.

Can you explain the advantages?

All the advantages are things you are not interested in for sure. 😛 (And I knew that from the beginning. 👼 )
It's the usual trade-off between me and you, but now I have other things to do, we will fight another time.