I think 3rd party apps and external websites is absolutely the way to go now with any community-based initiative. For one thing, as people have mentioned, these forums are not what they once were. When the GMP began the forums were the only place where explorers shared their adventures, discoveries and travel blogs. There wasn't any API plug-ins, no apps, and as mentioned, no EDSM when the mapping project began.
In fact the GMP was a very crude and grassroots kind of thing, meant for a very niche crowd of avid explorers back in the early days of Elite. The original maps themselves were simple screenshots of the in game map with POI markers hand painted onto them! (some are still archived on the GMP thread somewhere). Very quaint stuff.
About a year later Corbin Moran created the high-definition galaxy map that everyone uses today, and shortly after EDSM came along and offered to host the project, and it flourished. But like Distant Worlds, no one had any idea it'd grow into what it became.
Inclusiveness as far as usage goes was very much what I wanted for the GMP from day one though. So it was always going to be forum based, even when EDSM came along. You didn't need an EDSM account to submit stuff to the GMP for example. I adopted the same policy with DW1 too. No third party website for that, or off forum registration process required, and it worked because it became the largest in game event of its kind at that time - probably because these forums generated massive amounts of traffic at the time and its where the majority of player hung out (something the GMP had tapped into a year earlier). DW2 was different, we had a website for that, and a rudimentary google doc application form for sign-ups, purely because all indications early on were it was going to dwarf DW1, and it did. But the actual expedition outline, WPs writeups, and news updates all remained forum based. And it worked.
But as I mentioned, today I think using all the 3rd party resources people have since set up, and discords etc, is definitely they way to go. People are massively used to them now, and they're perfectly tailored for this kind of stuff.
I really like the way GEC is going about it. Its modern, its easy to use, and its exactly what was needed to reinvigorate and bring fresh ideas and eyes to a project that is/was becoming a relic of the past (imo).
