I feel like Nextcloud is going to become Google one day, but I have nothing to back that up other than they just keep adding more and more capabilities
As long as they remain open source I see no problem with that.
I use both in my server and they're both great products, with the plus that you don't have to deal with any of Google's shitty practices.
Maybe he was talking about capacity to develop further or fix bugs. In theory a community can do that (and actually do in many instances) but sometimes development of a community fork tagnates due to the lack of resources.
Best example to disprove this theory is ... Nextcloud. Owncloud went ahead and developed a new version in go to scale more easily but next cloud is the defacto standard for most people that were using own cloud before the fork.
Adding a managed services option for NextCloud would be smart. Individual instances that don't share anything, managed by NextCloud and deployable on multiple cloud infrastructures.