I do not feel that Ubuntu threatens Fedora. What would threaten Fedora is if Canonical actually got so heavily involved with upstream projects that upstream development roadmaps for important subsystems like the kernel or Xwindows or GNOME were driven by Canonical's upstream activity.
I feel that Canonical as a corporate entity is a poor example of a corporate citizen of the larger ecosystem of open development and is exhibiting behaviours that negatively impact sustainability of that larger ecosystem. I point out those specific behaviours which need to be addressed. I will continue until those specific behaviours change.