I've permanently solved The Wanderer's Minuet problem...

[Reynhart]

1. They could restrict us to stay in some small area (like BLM)
2. They could make WM disappear when I start moving, so I need to reapply it again (probably with casting time)

If you know you have to move, you can just cancel WM so you will DPS as usual. And they even allow you to put it on back instantly, since 3.01. If you don't know you have to move and blame SE for how you don't manage WM properly, it's on you.

2. When I have a straighter shot proc, I can't use it immediately. I have to spend one more gcd with some skill (mostly with other heavy shot, getting other proc and losing that proc in that case)

There's almost one second left on you GCD when you finish casting Heavy Shot, how do you miss the proc ?

3. Why when I use repelling shot as oGCD skill, my next GCD skill can be interrupted when I wasn't moving after that?

Because Repelling Shot makes you...move, maybe ?

4. Why after I turn off WM I still have casting time on my next GCD skill?

Because you probably start your next GCD before the icon disappear. Exatcly the same activation/deactivation delay as every other oGCD skill.

[vp_cmc]

If you know you have to move...

So.. Why they decided to add casting times to WM and not taking any other possible approach? Causing those 1-4 issues?
And I usually don't know that I have to move, because it seems that SE started to love random-target aoe's in 3.x, so you never know. (a3s start for example. sometimes I don't have to move at all, sometimes I have to make a quarter of circle around a boss then move back before 2-nd attack).

There's almost one second left on you GCD...

Try this yourself.. Cast heavy shot under WM, catch a proc and press straight shot. Proc will not be used and cast will be not instant...

Because Repelling Shot...

I start next gcd cast after I moved. You can't start next heavy shot while still moving in repelling shot because of animation lock

Because you probably start your next GCD before the icon disappear...

Maybe this. So what then? Turn it off, then wait? Doesn't look like smooth gameplay to me.