it might not that trivial to solve but I would prefer to keep all at one place, meaning in this forum.
As the proposal is a private thing between the applicant and the organisation, I suggest that we create a group GSoC-Mentors and the applicant PMs the group. The applicant can but not have to draft its proposal as PM (using markdown). It is allowed to switch to google.docs etc. by sharing the link.
how does that sound?
that would may solve this too. The draft can be started once by telling the group and updates come by reply (as soon as there is structure recognizable)