And while they haven't announced the platform itself to be open source, I'm glad they're at least already contributing some of the stuff they're making [1].
We do not want to lock anybody into our service, so you'll always be able to download Typst for the command line for free. Only the web app will remain proprietary.
Most likely something simplified will start out convenient and then accrue much of the complexity of LaTeX over years (because that is solving actual needs!) -- the only difference (pro) will be that new users will be slowly onboarded to this complexity over years and (con) have to wait a long time for this to catch up with necessary functionality. An interesting example to observe is Markdown variants thrashing around and diverging as they try to go beyond the simplest case and try to model the essential complexity of writing documents.
> We will publish Typst's compiler source code as soon as our beta phase starts. From then on, it will form the Open Core of Typst, and we will develop and maintain it in cooperation with the community