That's not how banlists work. Banning Dark Void as a separate entity suggests Dark Void is broken, which it can't be while better Sleep moves exist and are not considered unbalanced. The only way this proposition would fly is if all Sleep moves are banned on all Pokemon for being overpowered. As long as Darkrai can use Dark Void and still be a grossly effective sweeper after the fact, he's bannable material.
Erm...
Banning Soul Dew as a separate entity suggests Soul Dew is broken, which it can't be while better boosting items exist and are not considered unbalanced. The only way this proposition would fly is if all similar items (that is Light Ball, DeepSeaTooth, Quick Powder etc) are banned on all Pokemon for being overpowered. As long as Lati@s can hold Soul Dew and still be grossly effective sweepers after the fact, they're bannable material.
...oh wait. Also, about the 'implication' that Dark Void is broken... who actually gives a shit? I mean really, who cares what it 'implies'?
If you're going to argue with me on principle, your concept still falls flat. You're proposing a blanket ban on a move that only one Pokemon learns (save for Smeargle) while said move is not broken in and of itself. That's not a blanket ban, that's just banning the move from Darkrai using different words. So really, this has absolutely nothing to do with Dark Void, you just don't want Darkrai to be banned. -_-
No move, item or ability can ever be broken 'in and of itself'. Soul Dew isn't broken 'in and of itself'; there are plenty of pokemon that if they could hold it would be prefectly fine, and not broken.
Also, those 'different words' are precisely what makes the difference here. If we were to say, 'Darkrai may not use Dark Void' then that opens the door to 'Salamence may not use Outrage' et al. But if we say 'Dark Void may not be used by any pokemon', that simply opens the door to 'Outrage may not be used by any pokemon', which is never going to happen since there are many pokemon that learn Outrage which are completely fine with it. Yes, I am aware that in Dark Void's case the former and latter ways of going about the ban result in the same thing, but the important part is that the first way is absolute and leaves no wiggle room for more complicated bans, whereas the second does. Do you not see the difference? If we outright ban Dark Void, there is no possibility for someone coming along and saying 'emmm can't we ban Outrage on Salamence??' since we've not banned Dark Void on Darkrai, we've banned Dark Void.
Of course this is to do with Darkrai rather than Dark Void. But in my opinion, removing one move from one pokemon's movepool in a way that prevents a slippery slope is 'less of a ban', so to speak, than banning said pokemon outright. And since in Smogon's Philosophy we aim for minimal bans, banning Dark Void would be more desirable than banning Darkrai.
As an aside, I'm fully aware that Darkrai may still be broken without Dark Void; however, I think that Dark Void makes enough of a difference (since it's on basically every Darkrai moveset currently) that it's worth a test to see if it's still broken, rather than using uninformed theorymon to state that it's not worth a test.