Yes but the scores wouldn't count against rankings or league standings.You mean like Blues or Surf Cup?
This is what keeps clubs from participating in cross league play. Everyone worries about maintaining or overtaking other league/club status.
In essence if ECNL/GA/ETC did SY showcases but CY leagues and all showcases were open for anyone to attend you'd end up with a tournament of friendlies. Which is what you want if the goal is to highlight player performance not team performance.
I'm sure someone will try to track wins and losses at showcases/friendlies but it wouldn't really work because teams are only put together for that specific event.