I've done something like this...not convinced it was a good idea though
So we did something similar to what you're describing at my previous company, where we had a "throwaway" branch where people could just quickly push their changes for demoing purposes. It was understood that this branch may be unstable and contain bugs. I'm not entirely convinced that it was helpful to have this sort of process in place, but I'm not going to discuss the merits or pitfalls of the approach in this answer.
A solution to overwriting other developers' work
One problem of this is, since people will keep dumping their code here, there is no guarantee your code will stay their as you initially committed ( others can overwrite yours ). I'll tell other folks about the purpose of this branch/instance and don't point this for release QA, etc.. but I'm wondering if there is any simple solution for this situation.
If you're worried about people overwriting other people's work, you can disable force pushes for an entire repo by setting this in the repo's git config:
# In repo
git config receive.denyNonFastForwards true
You could create another remote instance and set that config, then have your developers push a copy of their work to a shared branch there. It's still possible to "overwrite" the branch by deleting it, then pushing your copy of it, and there's a setting that will disable that in an individual repo too, receive.denyDeletes
, but disabling remote branch deletion can make it inconvenient for when you actually do want to delete the branch remotely...so I guess that's up to you.