The article doesn't go into how to integrate TypeScript in the monorepo for development - what we do on the Yarn repository is that we point all the package.json `main` fields to the TypeScript sources, then use `publishConfig.main` to update it to the JS artifacts right before being published.
This way, we can use babel-node or ts-node to transparently run our TS files, no transpilation needed.
Yeah, I would be interested to hear from others how they accomplish this. I played around with Nx and it uses TypeScript project references. It is a lot of boiler plate to set up every time you want to create a new app or library. Fortunately, their generators do this with one command.
Moving forward, I'm going to use wireit for these things. Pure modules get built with tsc. At the highest level (e.g. where it needs to be embedded in a page), make a bundle with rollup.
wireit has two nice properties: incremental building and file-system-level dependencies. Within a repo, you can depend on ../package-b. However, if you have multiple monorepos that often get used together, you can also depend on ../../other-project/packages/package-b. No matter where in your tree you make changes, wireit knows when to make a new bundle.
I've just started with wireit (it was only launched recently), but it seems to be a nice solution to wrangling dependencies between related JS libraries.