I will start with the TLDR. MMR can be though of as a Percentile system. For the most part you can expect about 50% of the games population to be near its starting MMR value or below. Inactive accounts + soft resets will affect this but not all that dramatically if theres no change to starting MMR. the new start point is iron. Expect to see a lot of lower MMR accounts this year.
This year riots new starting MMR is iron. They did this because folks are silly and whined about new players being in silver. A bad player, a complete newbie on your team? That sucked. No doubt there are some game losingly bad players out there and its not fun to have them on your team. But law of large numbers had your back in prior season. Any game your not the weakest player the worst player in the match is favored to be on the enemy team. You occupie 1 slot on your team so RNG favors you to have the worst player on the other side. Basicaly if your averaging 50% winrates in old silver over 200+ games you belonged there and that was with you having something like 20% advantage for the bronze and troll players being on the other team. That advantage is gone.
How ever, you still have every player that's new(and fantastic at this game some how, might be a dota 2 player or just inherently good with mobas.), smurfing, or just got a lot better at the game by finding a good main or mastering a mechanic they needed to set themselves up going thru these MMR despite newbies starting in iron. Bascialy Silver to gold will now have every player actively climbing because they are overskilled at a higher % odds to be on the enemy team and there is a drastic reduction of having a completely garbage player on the enemy team giving you free wins.
So the entire ranked ladder is going to shift down. Bronze is gonna end up in iron, some silver is gonna be iron. Gold can drop as far as bronze or low silver.
throw in some preseason mayhem with a high # of players trying to climb off luck of the draw rather then skill (best time to climb with luck is with a soft reset because theres a higher # of mismatches from MMR resets and everbody has a higher K factor for their adjustment. Kfactor is a term from Elo systems that's used to represent uncertainty. Higher the K factor the more MMR an account can gain or lose after a match. ) And its gonna hurt for a bit for every player in a mmr they are considered representative of "average" level of skill.
End of the day, not a huge change. Adjust your expectations for how skilled each tier is to be higher and your set. Ultimatly If your good enough you can climb to the top. A massive % of everybody will never EVER get that good and see this thou. MMR does not reward you for playing if your not getting better or not grossly over skilled.
