I'm not sure if I entirely agree. There's a lot more information on the proposals in this topic than most mods usually provide, and having a more standard way of providing that information would be helpful, even if it's mainly portmod which makes use of it.
One way of providing reliable mod identifiers and versions would be to set up an append-only metadata repository (sort of like some software repos like pypi.org or crates.io) which, for the sake of making it easy to add to, only requires the identifiers and versions. It it stores the versions in chronological order that should deal with version comparison issues (which occurred to me when you mentioned dated versions). I feel like there may be exceptions where there are backported patches released for old versions of mods, but this practice is at least far less common than for software, and I can't think of any examples.
But setting up a metadata repo which can be easily contributed to by mod authors would be complex, and I'm not convinced it's significantly better than just listing the mod name and compatible versions in the metadata file.
I've never actually looked at the fomod spec, but it bears comparing, as I don't think this is very useful unless it provides significant benefits over that (the actual spec is a pain to read, but the tutorial gives a nice overview). My conclusions:
1. The fomod spec provides only a formal installer spec (ModuleConfig.xml). They have a suggested spec for info.xml, but only include name, author, description, version (they recommend semantic versioning though!), website and id (unclear).
2. Fomod is an install wizard format and probably isn't entirely compatible with a system like portmod which has its own way of handling optional features (it defines install "steps" rather than features/patches).
3. As far as I can tell, while there is a standalone validation tool, there is no standalone installer. While I don't think most people would care too much right now, it means that it's only useful while mod managers directly support it. But if there was a standalone installer you could still use it as long as that works.
4. It's an xml-based format, so it's neither easy for humans to read, nor easy for humans to write, and the only WYSIWYG editor, the fomod designer, is abandoned and incomplete. On the other hand, a yaml or toml-based format would be much easier to write manually.
I think it's also worth noting that even getting newly released mods to provide metadata would be a huge benefit. The nice thing about old abandoned mods is that they don't change. Portmod, for example, only has to package them once, and users don't need to update them, since there aren't any updates (at least, unless they get revived, either directly, or by a different author). Plus, it seems to me that people are mostly interested in newer and more actively maintained mods anyway (though this is mostly anecdotal I'll admit).
Do you think that support for the original Morrowind engine would also help? I think we should be able to use a BSA-based VFS much like how we're handling Oblivion and Fallout NV/4, though there are more files which can't go in Morrowind BSAs. I think we're more or less at the point where it would be feasible (there are some changes to the repo code in openmw-mods which will be necessary), but I have no idea what sort of interest there would be.
If you want to create .pybuild files for your mods that would be helpful.
See the package development guide, and openmw-mods's CONTRIBUTING.md for details about the format and the packaging process.