I'm going to have to disagree with you on some parts. The to 179th St and via Hillside Express was going to be a problem from the start since, let's face it-it's the . Today, you could get away with de-interlining by extending the instead to 179th St in place of the . Which actually would have made more sense when the was around.
To the & swap, I don't know who's smart idea it was to have them grouped like that in the first place, especially being that they share the same CPW corridor.
Going to the extension of the Astoria Line to LGA, the extension would work yes, but you make the problem along Broadway even worse with way how the is designed to operate by crossing in front of 's and 's. This is where deinterlining comes into play. You can waste all that money extending it to LGA but forget to fix the major problem that plagues the today.