Thanks, aek, for drawing attention to a skill that is becoming more commonly practiced.
>>> Let's consider formation flighting. Not in an ICAO-defined formations, but of much closer, like that on aerobatic shows. That's very dangerous business <<
It can be........ if it is not taught and practiced thoroughly. Its original concept was the passage of a number of aircraft together as a single unit. This was instead of the problems and increased collision risk of transitting each aircraft separately and trying to recontact just before reaching the combat area.
My feeling is that, if you need to consider other separators besides the Mk 1 eyeball, maybe you should leave it alone.
What would be your real reason for attempting it other than to try and emulate what you see at airshows ? Formation flying is not for "showing off". It is all to do with flying discipline and is a very skilled practice.
Having said that, there are a select number of clubs, schools and aircraft-specific groups that are available with very skilled instructors and very competent formation leaders in the UK should you wish to become further involved. Then you might see why a number of the thread contributors are uneasy about "autopilot formation", the complete antithesis of the reason for doing it in the first place.