FYI, we're in the (very slow process, admittedly) of updating the Theoryland system, and I plan on adding most of these features eventually.
Categories as well as tags. I would like to be able to just search through Cosmere sometimes, and not be distracted by WoT, or general questions about writing. Or visa-versa.
I plan on making the search much more comprehensive, including tag grouping, and tag trees, and the ability to search only in subsets of tags and all sorts of ways to make it easier to read/find only what you want.
Ability to browse a single QA session, or browse all topics in a single category or tag
This already exists for theoryland questions
Simple way to link to an source (i.e. Theoryland, TOR, etc)
Theoryland already has source links, including per-quesiton links (for twitter feeds)
Clean tool for entering a bunch of questions from a new event.
I will definitely be making it much easier to add/edit questions on Theoryland (atm the editing interface is dire)
In addition to categories and tags, an easy way to link related questions
I am up for suggestions on what kind of relations and displays and things are useful for future implementation on Theoryland
Anyone should be able to sign up for an account to contribute
I plan on making it a lot more open, with submissions for review by the Theoryland moderators (along with potentially adding edit submissions too) and edit history.
I also might add user-voting per question so we can find what are popular questions.
I know the feeling that you want a system that has all the bells and whistles, that is able to collate and display all interesting info in unified nice modern clean fun easy to use interfaces. But for one thing, you wouldn't be able to just copy all the data from Theoryland (en-bulk), because it's probably licensed to them, and it's also totally and utterly unfair to rip all their data after the thousands of hours they've put into it. And splitting effort (on input) between two sites just reduces efficiency and quality over all. I'm sorry it's taking so long to improve/fix Theoryland, but it will get done.