Somewhere down the line a bunch of money has to be made. For themselves and especially to make those VC folks happy (however 'patient' they are, according to their announcement). If they remain 100% open-source, their hosted servers may come with subscription (the Discourse model), and/or they may supply paid for professional templates and plugin packs.

But whatever their plans are in this regards, I think it would be good if they were more clear on their planned strategy.