I think yes, although I would like a standard format later on, but NIP-78 is good for experimenting.
Discussion
Reading NIP-78, it seems strange to me that it’s a NIP at all. Seems to be a strict subset of functionality already described in NIP-33.
Is it just to set aside kind=30078?
Yes, thinking about this, it would be nice to have a standard for theming, reusable by clients, otherwise there will be many events from different clients defining themes in a different way