You probably are well aware, but security wise that's a huge issue. If it's a hobby app, okay, but anything with actual users should separate keys. The main concern would be that dev keys are not considered secure and anyone with access to the dev key could then impersonate any other user of the production application.

I wouldn't want to share keys like that. I'd also lose out on being able to modify my test account(s) with different groups/permissions that might not be in production yet.