M1 - I don't see harm in that, especially if you were to add LTD service on the M3 as there would be at least one 5th Ave route that is fully local..
M2- Idk how M2 LTDs are, so I can't comment on that, but considering that it is only LTD between 14th and 110th, it shouldn't be too bad but see my part about the M3
M3- If you are going to make the M2 LTD rush hours only.. Give M3 LTD service 7 days a week (as the M2 has now) just to supplement weekend LTD service along 5th/Madison...
M5 - leave it how it is, LTD service ends at 8th St and the M4 can't supplement lost M5 LTD service as it ends at 34th St
M7 - That would make the M7 fairly long wouldn't it? (not as long as the M5, but pretty long) and considering that the M7 doesn't have LTD service (at least the M5 does) that would make it a long trek for the B/Os on that route... Also may I mention, the M20 gets caught up in Holland Tunnel traffic sometimes, so that may cause delays, so I don't think that the extension would work, but I see what you are trying to do...
M10 - Having the M10 service 9th Ave isn't such a good idea, its like the same thing as the M7 idea... The M11 now gets caught in Lincoln Tunnel traffic between 34th and 42nd, so that may make your M10 a delayed route..
Discontinuing the M20 is going to cause riders in Battery Park City to lose their one seat ride to Chelsea, areas like that on the Upper West Side, and I don't think that is such a good idea... But on the bright side, they would have buses that are more frequent then they are now. The M7s headways are 7-12 minutes during daytime hours (including weekends) and the M20's are 15-20 minutes.....