There are definitely a few unfortunate shortcomings with Solid as an ecosystem at the moment:
The default web UI, apart from the login process, feels really clunky. Some clever CSS could probably completely fix this.
It looks like it's still rather difficult to host your own pod server; they say it's possible but don't tell you how to do it, instead just saying it's not for the faint of heart.
It would be great if I could connect a local file server, maybe even one hidden on a local network, or host on multiple pod servers for redundancy of my own data.
Is there a way to set up multi-factor authentication or Passkeys yet?
Other improvements I think could be made:
A server's home/login page should list a few apps, perhaps configurable by the server administrator (...within Solid itself, of course). A file manager, Penny, and an inbox viewer would be great here.
I feel like setting up the inbox as one append-only Resource would be a good idea. Or, you get even more advanced with the ACL, and have it so that each authorized app can see all its own inbox entries.
Someone should make a Solid file manager plugin, maybe even with metadata support, for Nautilus and Dolphin, at least. You sign in and authenticate with your pod server, and your available Pods all show up as network filesystems (if there are multiple, they should probably all not be on the sidebar, but if there's just one it's fine).
Seeing as it's been in development for 8 or more years and it's not out of the experimental phase yet, I don't expect it'll ever come to light, but if it does, yeah this could very well change the world...!