I really appreciate your work on it @linonetwo. The plan is to explore adopting your changes as part of a complete rewrite once I find the time. The very first versions of Streams were heavily macro based but changed to transcluding tiddlers instead because of drastic performance differeneces. Since then I believe we have mitigated most of the performance differences but some testing will be needed to make sure that we have no regression in this regards if we switch to using procedures. I am also holding off on a Streams rewrite until some things land in the core, like better localization support and improved palettes.
I have experimented with this and use it in one of my wikis, and it also entails changes to streams to remove the distinction to some extent between editing and view modes. This is another area that I want to address in the Streams rewrite.
The Streams rewrite is planned to be entirely backwards compatible for end users, but not for plugin writers or advanced users that have customized the plugin. Therefore, the plan is to one such breaking change with a complete rewrite rather than piecemeal. Once I find the time, I will make a post with the issues that I am tracking that I want to explore or address in a Streams rewrite.