I like the addition of the descriptive subtitles. But I would suggest taking them to meta to settle on what they should be exactly, and also then documenting them (including arguments) to make sure that they can be used consistently throughout the projects.
I was wondering about the colors. Have we considered the MediaWiki/OOjs UI color theme already. In my opinion the portal feels more cologneblue than Vector right now..
Also, I do wonder a bit about the consistency of the portals and the lack of options for reuse of these improvements by other portals, and I personally think it would be great to start expanding parts of the development to other portals now.
I think it would be wonderful if we could create a pipeline of reusable elements among the portals, that allows for some consistency, but trying to avoid blandness and uniformity. Simple things like a library of Less variables usable by all portal pages can mean a lot for these kinds of efforts and I'd love to see some attention devoted to that, so that other portal pages can benefit.
For community participation, I also have some ideas:
1: There is no README.md
2: Make sure that it's easy to test the master version.
The great thing about github for instance is that you can do tricks like:
https://cdn.rawgit.com/wikimedia/portals/master/prod/wikipedia.org/index.html
That's powerful to be able to preview straight from a git repo. If you have links like that to the readme/meta page.
3: Update https://meta.wikimedia.org/wiki/Project_portals <https://meta.wikimedia.org/wiki/Project_portals>