Removing 'old Pym' would be a mistake, in my view. There is now a surfeit of superhero films, and in the crowded market, each film needs it's own take that makes it stand out. Marvel cannot release a film based on the well trodden path of hero origin - villain reveal - hero v villain fight.
What Wright's Ant-Man had going for it (for the general audience) was, firstly, Wright. Secondly it had an interesting story about an older superhero who was out of the game, a younger criminal who needed to become a hero, and the meeting of the two to win and gain some redemption. The former has gone, the latter (hopefully) remains.
The elements reminiscent of Obi-Wan training Luke or Zorro passing on the mantle, added to the 'to steal an ant-man' narrative of the little guy going against a big corporation to save his daughter (the David and Goliath analogy) made a compelling stand alone story. Further to that, the idea of an elder statesman scientist being introduced to the MCU, a guy that Banner and Stark could both look up to, adds more dimensions to the universe. The universe would then contain a good cross section of heroes, from the older ones who have mentoring roles (Pym, Fury, Odin), through the heroes at their prime (Barton, Romanov, Stark, Banner, Cap and Thor) to the young, new heroes just discovering what they are capable of (the Maximovs, Lang, maybe Vision).
That idea is what I was looking forward to, this film was going to be a new angle on the superhero film, one that looked at the idea of legacy, and passing on a torch. I'm disspointed it won't be directed by Wright, but I'm hoping the ideas that were hinted at are borne out and that we get an interesting, self contained narrative with strong characters performed by top drawer actors.