Path of Exile has skill respec items (unlimited), respec tomes (limited) and full free respec every 3 months.
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Personalily speaking, my dream would be for Blizzard to make a Diablo MMO that is more or less the gameplay of Burning Crusade Era World of Warcraft but with Path of Exile/Diablo 2 systems.
I like 2nd wave MMORPGS such as World of Warcraft but I always disliked WOW's aesthetic, lore, structure, etc. Something between Marvel Heroes 2016 and The Old Republic would be perfect for the Diablo franchise for me.
I am not saying this a realistic or possible direction for Diablo. Though I have personally wanted a Diablo MMO since the original Diablo 1.