The reason those missions were cancelled...
was because the price for each was spiralling out of control, the same as with so many other NASA programs over the years. I sincerely want those missions to fly but not at any price. We've already seen with the ISS and several other programs what happens when cost discipline gets pushed aside by go-fever. NASA management will have to get past their "if we built it, it doesn't matter what it costs" mindset.