I can tell you what is my idea about this. My interest in having a GNU
kernel for the GNU operating system has nothing to do with technical
aspects, but with polithics.
The Linux development is managed by a person who doesnt agree with the
ideals of the free software movement. I cannot trust that
person. AFAIK the copyright holder for Solaris is SUN. I cannot trust
that company.
That is a good reason for us to wish for a successful GNU kernel. But
that won't MAKE a GNU kernel successful among users that don't share
that wish. For that, we need to achieve impressive practical
advantages. Any sort of practical advantages could do the job, but I
think the main areas where the Hurd has a chance to achieve them are
in security and flexibility.