It depends on what you mean by "significantly diverge." If you mean "innovate", then yes -- absolutely. We already have tons of evidence of differentiated innovation in illumos[1][2][3] -- none of which can be brought back into Solaris.[4]

[1] http://blog.delphix.com/matt/2012/07/11/performance-of-zfs-d...

[2] http://dtrace.org/blogs/bmc/2012/06/07/dtrace-in-the-zone/

[3] http://dtrace.org/blogs/rm/2012/07/16/per-thread-caching-in-...

[4] http://www.youtube.com/watch?v=-zRN7XLCRhc#t=43m55s