reason to fork the kernel ?

The culture war between those who want copying easy and those who want it difficult in specified cases isn't going to go away, because major industrial and commercial interests are on either side of it or, in some cases corporations e.g. Sony have divisions on both sides of this conflict of interests.

The kind of DRM support one kernel could provide can't fully support both sides of this war, in my view. If so, the solution may have to involve forking it. GPL3 enables DRM to be included but requires the end user to be provided with a copy of the keys, so the end user can still benefit from DRM, e.g. by helping secure their system for purposes agreed with by the end user, while retaining freedom to change things when and as required. GPL2 enables DRM to be included where no such requirement exists and freedoms to modify and study previously intended through the GPL license can be barred.

The problem will be with those intending to develop a GPL3 fork having to start pretty much from scratch based on parts of the kernel for which contributors are willing to make contributions available under GPL3 only, or BSD, or public domain or dual licensing compatible with the GPL3.