Quick post from my phone to get things back on track
Speaking for the council here: Making some kind of NatDex DOU ladder is not really on our radar atm. Our big focus is making our current actual meta as playable as possible. Making one with mega stones and Z moves will absolutely never happen.
Nerfing or even outright banning dynamax is on our suspect radar, so please stop assuming it isn't :). This isn't the only possibility we are discussing, but it is one.
Speaking for me here: I would love to get the SM DOU ladder back but I think it would be a hard sell to the guys who run Pokemon Showdown. Presumably if you ask they will say "DOU is no more important than lower tiers and we are not adding back 7 inactive ladders (UU through PU, LC, Ubers, DOU)." If you want to keep fighting this fight, somewhere in the Pokemon Showdown forum is the place to do it, though I'm honestly not sure whether it belongs in Suggestions or Other Admin Requests.