I think you're pretty spot on in your analyses though. We use static sites for our landing pages (currently using Jekyll, Grunt & S3) and I can't see a real reason to switch to something like this.

From a business standpoint I worry Forge will have a really hard time building a sustainable business off of $10 / month / user. That's a lot of users they'll need to build something profitable. There is likely room here though for add-on services or some unique features.

Curious to learn more about TurboJS as well.