Aerotech,
We (EK) operate 777s using up to the maximum 207min ETOPS, so I'll attempt to answer you questions.
1) For twins, defiantly. We operate Polar routes when going DXB- US West Coast that would be impossible without 207min ETOPS.
2) I believe 207 is the longest currently in use. I did read that Boeing want to certify they 787 to longer (329?). If that came to pass, I don't know if similar certifications might become retroactively available for earlier types.
3&4) There is rarely any problem with ETOPS fuel reserves. Typically, a flight goes from one populous center (in our case the ME) to another (USA), passing through remote regions necessitating ETOPS. As the aircraft is obviously carrying fuel to complete the flight, normal fuel loading easily covers the extra requirements to cover the 1D, 2D and 1E diversion requirements during the ETOPS sector. ETOPs fuel would only be a factor where the ETOPs sector is near the end on the intended route.
5) Yes those plans are in place, I am not aware of it causing any restriction to growth.
6) No. Modern engines and systems are incredibly reliable.
You seem to be a little stuck on ETOPs fuel reserves. They are a small and, as I've explained, rarely limiting part of ETOPS. Lack of suitable airports within the 207min threshold is much more likely to effect the viability of a route (I believe it had a part in making PER-JNB non-viable for V Australia as they had to follow a non-optimum route over the Indian Ocean).
Increasing the ETOPs threshold beyond 207 would make new, more efficient routes available.