The first thing I'll say is that if it would be helpful, I can have an example of a real dit (showing real syntax, the way labels change on the fly, etc.) on https://www.ditabase.io/example in a few hours. I only didn't do that to save some time. Thank you for expressing interest!

So these are all questions I can answer:

1. How do I pull this into a project?

Assuming you have a dit that you can use (full of scripts and such that you need), all you have to do to use it in a project is use existing infrastructure to tell the dit to validate itself, convert to something, query the data inside, etc. The plan is that this would all work with a linux app. I suppose a repl code interpreter would also be convenient?

dit validate workspace/assets/example.dit
dit convert workspace/assets/example.dit "sy7QvPp9" //UUID of the schema you want to convert to.
dit query workspace/assets/example.dit "LengthEnglish" //Lots of options, etc.

2. How do I access new dits?

All public dits would be available for free on the website. Anyone can view, reproduce, fork, pull request, etc. The starting dits would almost certainly be based on schema.org's object model. If you want something specifc, you could start at say, the DitaBase fork of https://schema.org/Organization and then look at the most popular child schemas until you find what you're looking for. The whole concept is to function the way open source software already does. If someone wants to announce they've made something new, or ask for help finding something, they use exising channels.

Naturally, some people will want to keep their dits closed. In this case, they fork public dits and keep their own closed, using whatever project managment stuff they prefer. They never have to inform anyone how they are using dits, the same way you can start a new git project without ever informing GitHub or BitBucket or something.

3. How do I write a dit and publish it?

The same way you would start a new GitHub project, but on DitaBase instead. Create an account, start a new dit, and beginning adding whatever you need for your project. Every dit gets its own project page, and dits probably will not really belong exclusively to the original owner of the project, because for really popular open dits, they will get used by lots of people.

Of course, dits are not really like regular code projects, since having a public dit that isn't on the DitaBase system isn't all that useful. You can also imagine that you might want to use tools available on the website specific to dits, like pasting a dit and asking the site to check it for you, or attempt to convert it. It might show you a graphical map of the many different components of your dit and how those relate to where you want to convert to, and if a converter is missing or bugged, you can jump right to that page and start adding one, right on the website (many converters will be extremely simple).

4. Where is the source code? Is it going to be open source and free?

At the moment, there is no product. I'm only about a month into this project and I want to get feedback before I start going nuts making a product without hearing from anyone.

I intend for the overwhelming majority of vital DitaBase features to be open source. The Linux app for example, obviously open source. Any dits someone makes, if they want them to be, totally free and open source. DitaBase can make its money in other ways, such as providing all of this stuff as a service, and capitalizing on the new market advantages of DitaBase. In the long run, I envision a search engine that queries public dit repos, rather than just webpages, and can return data directly instead of just saying "Well, here are some webpages which probably contain what you want." So, yes, I want to challenge Google search.