I think, some regular-REL draft events are run by ‘Rare-draft’ prize scheme.
(Collect all Rares and Mystics (and sometimes foils) after the final round, and pick in ranking order)

The problem/question is following;

1. Is this scheme is allowed in Rated events?
   

If it is yes, there are is problem/question.

• If the player who wants to drop leave the event WITHOUT putting his/her Rares&Mystics, does he/she commit any infractions?
  MTR allows the player to own the cards “that they correctly have in their possession at that time”.
  

Does anyone have any opinion?

It is allowed, but it's not a great idea with Inventions; too many players (now) prefer “keep what you draft”.

If a player leaves early with their rares, there is no infraction from our (Judge) perspective. The store and other players might not welcome that player again.

d:^D