After the human Covenant war, I don't think I've ever seen a new ODST soldier in any of the books or games. And the Buck books give the impression that every current standing ODST with a decent military record was made into a Spartan IV. Does this mean the ODST programme was scrapped and everyone was either a marine or a Spartan?

A lot of human technology has been significantly improved thanks to the Forerunner advancements they've integrated into everything. I would love to see some new and improved ODSTs. Maybe some gravity powered drop pods that increase survival rates, or allow multiple soldiers to drop together. Maybe an advanced drop pod that can land a Mongoose or Warthog onto the field.