Fedora project switching to new contributor agreement

I'll answer that (as principal drafter of the Fedora agreement, and occasional observer of Canonical's Harmony group from the sidelines): None. The unique feature of the Fedora agreement is that it formalizes the right to opt out of the default license (MIT license for code, CC-BY-SA with GPL compatibility for content). The default license is granted by the contributor.

The draft Harmony agreements are, to my knowledge, in all their existing permutations, structured quite differently: Give up your entire copyright interest to one inbound entity (or grant a maximally broad copyright license to one inbound entity). In some permutations, but not others, certain conditions are placed on the inbound entity. Downstream licenses (if any) are granted by the inbound entity. There is no formalized opt-out right, unlike the Fedora agreement.

In the Fedora agreement, there is no named inbound entity - the contributor is understood to be granting the license himself/herself/itself, to (potentially) the entire world (anyone who might possibly participate in and receive material produced by the Fedora Project). Where the default license applies, it is a well-known, standard license. Those who want to opt out of the default licensing system and (say) GPL their contributions are encouraged to do so.

If experimentation with those two very different approaches is "proliferation", I welcome it.