You can legally invest into a new business with revenue from your existing business. What's not legal is running a line of business in a way that's inherently unsustainable.
So how is CloudFlare having a free tier not “sustainable” when that’s what almost every company does? Do you think the Google Pixel makes money selling only 800,000 phones a quarter? Would it be sustainable as a standalone company?
Is the “HomePod mini” a line of business? Would it be sustainable if it weren’t subsidized by the rest of Apple?
Are you starting to see how meaningless your definition is?
