That would be good, as the biggest drawback to HND right now is the lack of NEx-type train service. But I'm surprised that Keikyu/Toei metro hasn't tried to come up with some type of train service option with reserved seating and luggage space to get a major head start on things.

As JR is asking the public for hefty subsidy for this proposed project, a much cheaper alternative to building new train routes would be to bolster HND-Shinagawa service and then really develop Shinagawa as HND's gateway. This makes sense because, as it already stands, Shinagawa is so well-connected to most everywhere, and Keikyu-JR connection is very easy (they just need to install a few more escalators). Shrinagawa's got Tokaido line and now Tokyo-Ueno Line heading counterclockwise, but one thing that's severely lacking at Shinagawa is an express line that goes clockwise since both Saikyo and Shinjuku-Shonan veer off just above Shinagawa. So they need to come up with something like that.