As an open source contributor, in some ways this makes me much more frustrated than someone making a closed source fork of a BSD licensed project.
This would mean any model for which the trainer did not have permission to create a derivative work either implied by the work’s current license or obtained by them would have to release their model’s weights.
You could argue that it’s fair use, but a fair use quotation of a work does not become the property of the one quoting it. If I quote a line from a song or a novel I do not now own rights to that line. So there’s precedent for this.
I feel like legal frameworks sometimes lose track of fairness