All true, pros and cons to everything. A friend of mine just took delivery of his this week and is on a 1500 miles trek from CT to Atlanta with a few stops in between for clients. His trunk is full of gear but I think he left his S900 home for easy of travel and quality of video he can provide for these particular clients.
I've never been a big fan of modular designs as far as spare parts go and availability of them, especially DJI with new releases but they do seem to have a good thing going right now. I do like to build mine from the ground up so I can vouch for what is going on with my rig but sometimes it would be nice to just open a case and in five minutes be ready to fly. Yes there are issues with machine but if you get a good one it can be less stressful than all the tweaking involved with setting a bigger rig.
As far as GoPro vs DJI, I own a few Hero3's and like them to a point, never liked the FOV except at medium setting and that takes away some of the quality. ProTune stuff looks good but as SleepyC points out, they're made more for the sports world with a close focus vs DJI targeting the aerial market. I use them on a Disco Pro (although that wasn't seen much flight since the new build) and a F550 which is my daily flyer for now.
Think I'll wait for the Inspire2 since I never like to buy first generation stuff anyway.
That being said, I've got some batts charged and ready to go do some more testing, gimbal, FC, etc...