Says the guy with handle Ingo_Lutkebohle 
Jokes aside, from the google groups discussion I don’t really understand why the decision to enforce stricter rules in the first place was reached, but I haven’t really been following the developments as much.
In my opinion minimizing the migration effort by far outweights the consistency concerns. Consistency can be improved by having some style guide and linters to educate users and maybe even enforce the rules for new core messages. At the same time we should still allow exceptions, in particular also to accommodate non-public messages people might have. So for that reason I’m in favor to have the same rules as for ROS1, unless there is a very strong technical reason to change it (making constants easier to distinguish from fields is nice, but not a very strong reason but rather only a little bonus IMHO, especially since most IDE’s have syntax highlighting for that sort of thing).
For core messages like CameraInfo, I personally would only change them if there is a strong reason to do so and if there is consensus among a larger number of actual users of these messages that the new version is actually an improvement. For some suggestion of one person of a more consistent / understandable naming, there are probably 5 people that disagree or have their own alternative suggestions.