High MMR in Promos
After seeing the thread on reddit talking about the possible difference between your rank and the rank of the people you actually play with. Since there's no lock on how far MMR can vary this can lead to someone having to win 2 out of 3 games against Gold 1 players to prove they should be in Gold 4. So even though you gain LP faster to compensate there's definitely a bad feeling going into promos.
Which lead me to think that to compensate Riot should implement a setup similar to what promo helper currently does except activate it when your MMR is approximately 2 divisions higher than your current rank. So just being able to hold even against people in the division above the one you're fighting for means you'll theoretically be able to beat the people in the division you're fighting for 2 out of 3 games.
This was a pain point for me recently as well. I had to play my promos for Plat 5 against plat 2-3 players with good winrates. So while that high MMR meant it'd be easy to get back in my promos after a failure it's still a big waste of time and effort to keep trying. In fact my MMR was 2-3 divisions up all the way from Gold 2 - Plat 5.