Me and my friends skipped promos somehow. Like we had around 80LP, won a game and got promoted without needing to do promos. (Yes, we played the 10 placements before that.)
I have 2 ideas on when it can happen.
One of them is if your MMR is high enough, you don't need to do promos.
The other one is that in the divion you've been placed after the 10 placements you don't need to do promos.
But these are just guesses, can anyone confirm anything? I don't remember ever skipping promos in the old system. I knew you could skip divisions, but not promos. One of my friends even skipped the 5 match promo you need to complete to get to the next tier.
Edit: Someone in the comments pointed it out that you skip promos if your MMR is 1 tier (4 divisions) above your current rank.