How about this for the Ranked Ladder System?
If you've let's say played and won your promo from S2 to S1 and then end back to S2 from a cold streak, you won't need to play the promo again, but will simply rank up to S1 0 LP if you exceed the 100 LP required.
So if you're 95 LP and win a game, instead of entering a series, you are instantly promoted to S1.
This however is restricted up to the league itself, so if you drop from D5 to P1 you'll still need to play your promotion series to get back into D5