4. Over time such definitions would likely change. If you wait long enough, we’ll probably be considered Rishonim. Playing with the dates that periods began and ended in history is something historians love to do, especially with sufficently strong beverages to encourage discussion (meaning it is about convenience, not substance). I would argue that the period of the 1940s is a major “watershed” in Jewish history, and everything before 1940 is the “past”, and post 1950 is the “present” – and maybe in a few centuries people will see it that way.
People already see it that way. Personally, I treat any post Rav Moshe shittos very differently than those before (or Rav Moshe himself).
This is true with holdovers such as Rav Ovadia, and without saying Rav Moshe & the Chazon Ish. It may become similar to Rav, who was both a Tanna & an Amorah.