Geoff said himself:
As a Reaper main, I am hype as hell right now!!! What about you guys? What could the buffs be? Oh man, I am Flipping out!
EDIT: I will add that this was stated in response to Geoffs concerns about a tank META incoming. So that suggests that the buffs to Reaper and Mei might have something to do with them being better at fighting tanks.
spread decreased by 5% and shadow step takes 1.8 seconds instead of 2
“massive success”
Not about the Mei buffs, but about the Reaper buffs - I am PUMPED
He also said this:
This implies that if the meta doesn’t end up going towards tank meta then Hog, Zarya, and Ana will be buffed. To him it feels like those 3 heroes are on the weaker side but won’t buff them if the meta turns in their favor…but if it remains dive heavy then who knows