Preseason MMR/ELO

Hey so I was thinking, in every other season, the preseason lasted a month (season 6 ended nov 7th and season 7 started dec 8th), back then, the mmr u had in preseason mattered very little in the positioning games and those were mostly determined by the MMR from the previous season.

But this year is quite different... Correct me if im wrong, but this preseason is gonna be the longuest one ever since season 8 starts around 10th of January. So, how is the MMR we win/lose gonna affect the mmr we start season 8 with? Is it gonna matter a lot? Is it gonna matter the same as other years?

I think it should count more than previous seasons, since its gonna be 2 months of playing.