Back in November there was experimental DRI PRIME support for Wayland
via a set of Mesa graphics driver patches. Those patches have now been revived for multi-GPU rendering support.
The second revision to the Wayland PRIME patches for Mesa are still flying under a "request for comments" flag and implement DRI PRIME support in full to allow secondary GPUs to provide rendering support within the next-generation Linux display server.
The patches also provide the benefit of allowing the drirc file to specify the GPU for rendering rather than relying upon the DRI_PRIME
For good rendering performance on a secondary GPU with Wayland, the other GPU should have an embedded Wayland compositor on the other card where the application should be launched to, so that the application can render to a tiled buffer and the compositor then does a linear buffer copy to the main Wayland compositor.
More detailed on this revived DRI PRIME Wayland Mesa work can be found via the new patch-set on the mailing list