This makes Dacks Emblem able to steal planeswalkers now.
Couldn't you already do this? With an Emblem out, Pyroblast a Planeswalker, and you get to steal it? Obviously the Pyro shouldn't kill it, so either you Pyro a non-blue Planeswalker or you counter your own Pyro?
If Earthquake no longer impacts Planeswalkers then this is a big hit to the Baral Burning Wish deck. Also, the most iconic anti-Jace card of all time, Blightning, now does nothing?
This change is nearly as big as the stack rules change or the mulligan change... so many changes
Side note; Earthquake is better than Rolling because you kill Zombie tokens but not Narcomoebas.
By the rules above, Blightening should still be able to hit planeswalkers. The discard 2 cards is not part of a calculation or information used to determine damage. Its simply a secondary effect of the spell. A player with 0 cards in hand can be targeted and damaged by blightening so there is no reason a planeswalker couldn't be. And the discarding 2 cards has no affect or bearing on the damage done to the player. I guess we'll have to wait for the errata to be sure, but from the rules above, blightening should still hit planeswalkers.