I've crossed Crib Goch well over 100 times but I have also slept up there a few times as well, including once in the ice (not recommended)! There's not a lot of space, and you definitely won't be pitching a tent on the ridge, but for one person in a bivvy bag it's perfectly doable. However, you'll be sleeping about half a meter from the edge of a 90 meter drop so I don't recommend wild camping there if you're not very sure about what you're doing, or if you roll about in your sleep a lot. Also, it's probably not worth doing in the summer because there will be a constant stream of people passing you, day and night, so you wouldn't get any sleep. And if someone isn't paying attention they could even step on your head!
My First Wild Camp Up On Crib Goch Ridge - 22nd April 2015
You can't beat climbing up to Crib Goch on a sunny evening with absolutely no one else around!
23rd May 2016
A year later and I wanted to sleep up on Crib Goch again! Great weather, and an early start to get to Snowdon summit and have it all to myself.
24th March 2017
Slightly different this time; I went up to Crib Goch and slept out on a sheet of snow and ice. I had two carry-mats which did an excellent job at insulating me from the cold. Waking up in the morning was a bit daunting when I realised that the bowl shape that I'd been sleeping in was now glazed over and incredibly slippery. I'd also made the school boy error of leaving my boots out so they had turned into blocks of ice. Fortunately it was a sunny morning so I could thaw them out whilst waiting inside my sleeping bag.