I don't have any fears that Diablo 4 will be pay to win. I understand the mobile game being so, as pretty much every mobile game ever is pay to win garbage. But I feel as though they'll be careful with Diablo 4, especially after Diablo 3 and the real-money auction house they had.
(Which, by the way, I rather liked. I made a good hundred dollars off of it before they shut it down! xD)
Yeah, I know a few who made money with the real money AH back then :D
But I still hope this will never come back.