Hi,
after discussion I post here my idea for patch / plugin / implement to the core.

IDEA:
All projects have define members

1) When I create new issue, all members of project will be set as watchers
2) When I change project from one to another, all members from new project will be add = for example: I have issue in Project A. Dave, Mark, George and Diana are members = watchers of Project A. I edit an issue in project A and change project to Project B. Only Frank and Peter are members = watchers of Project B. Result is: Dave, Mark, George, Diana, Frank and Peter are set as watchers for issue, which move from Project A to Project B

WHY:
If you have many projects, where is few people (from 4 to 10 for example), it's really annoying everytime clicking user by user to define them as watchers. Solution by groups, when you click on group as watcher is OK, but is manual - so what if operator forget? This would be automatic.

WHERE TO SETUP:
Project > Setting > Information > "Do you want all members define as watchers for issues?" YES/NO
It will be easy to manage and all will recognize what does it mean.

Unfortunetly I'm not able to develop it myself. Let me know, if you want more discussion about this idea.

With best regards
David