I see it a bit like the camera bag and bush walking/ hiking day pack. It may have its place in specific purposes.
I have got a Tamrac Expedition 5xxx Series bag, great for putting all your gear in, stores in well, protects it, keeps it dry and safe.
But a rather horrible back pack to take on a day hike. Ok if going to the zoo or similar or just transporting all your gear. I much rather take my proper day hiking pack when going on any bush walk. They are much more comfortable and easier to use.
A vest might be great for storing all the stuff in, but is not really a jacket to protect you from the elements or to keep you warm and dry, alternatively you may just get too hot and want to take it off.
Good if you need quick access to batteries, cards and cleaning gear with the odd lens tugged in.
I got a pretty weatherproof resistant jacket with a top pocket that is fully sealed and generous side pockets as well as generous interior sidepockets that work really well. I can tug the 7D with 15-85 lens into interior side pockets and the 70-300 into the outside sidepocket.
Canon Powershot S95, Canon 6D,7D, Canon 40 2.8 STM, Tamron 24-70 2.8 VC, Canon 17-40 L, Canon 15-85, Canon 85 1.8, Sigma 30 1.4, 50mm 1.8, Canon 100 2.8L Macro, Canon 70-300L +Kenko 1.4 Pro 300DGX, Canon 430EX II and RS 4 Classic