Hi, I am a long time Pox player and reader of this thread, and I'd like to give my opinion on several returning questions here:
Regarding Dark Ritual: I have been playing with Dark Ritual in Pox for years and it always served me well. Pox is very mana hungry, especially for black mana. Lilly, Crucible and to a lesser extend Phyrexian Totem are excellent Ritual sinks, and it provides an opportunity for the dreaded Inquisition + Hymn start.
That said, I then played without Rituals for almost two years. Pox is a control deck at heart, and Rituals are clearly card disadvantage. It also worked very well, with a slightly increased number of 1-mana discard (5-6 instead of the usual 4, in any combination of Inquisition and Thoughtseize). Without Rituals, starting hands and topdecks feel overall stronger, but I think this is misleading as you often lack Oumph.
Right now I am back to 3-4 maindeck Rituals. While it can be a lousy topdeck, most of the time it fuels some powerful early game plays which can really put you ahead. Turn 1 Lilly or Crucible, double discard vs. combo or Engineered Plague are hard to beat for a lot of decks.
Regarding Sinkhole: Another card which goes in and out a lot. Like Ritual, i really really like Sinkholes, not just from a flavour point of view. Alongside Wasteland and Pox, there is the very real possibility of mana screwing an opponent. And for quite some time this worked and won games. In the current metagame the power of land destruction feels greatly diminished however.
I don't think this has primarily to do with Deathrite Shaman, but current decks are either packing more lands than previously (especially more basics) or they have better search capabilities to find missing lands. Combo decks can also safely sit on Fetches until they plow you out. So right now, Sinkhole is out. And with it also Nether Void.
Regarding Phyrexian Totem: I like the Totem enough to play 2 most of the time. It's an average mana rock for the often required second black mana, but it really shines as a clock vs. combo, empty hands and opposing planeswalkers. It's hard to get rid off and it tramples over those tiny 1/1 tokens.
My current deck list:
Maindeck
13 Swamp
4 Wasteland
4 Mishra's Factory
4 Urborg, Tomb of Yawgmoth
3 Cursed Scroll
2 Phyrexian Totem
2 Nether Spirit
2 Phyrexian Arena
2 Bitterblossom / Chains of Mephistopheles / Sinkhole
4 Fatal Push
4 Dark Ritual
4 Liliana of the Veil
4 Inquisition of Kozilek
4 Hymn to Tourach
4 Smallpox
Sideboard
2 Pithing Needle
2 Ratchet Bomb
1 Crucible of Worlds
2 Engineered Plague
1 Night of Soul's Betrayal
4 Leyline of the Void
2 Extirpate
1 Thoughtseize
I think one of the more unconventional choices is Phyrexian Arena. It's my card advantage engine of choice and it wins a lot of games by providing a steady stream of disruption. Does it kill you sometimes? Yes, but very rarely. It's questionable vs. opposing control decks (of all things), as for example Miracles is very able to parry any aggression and just let you die on your own enchantment. But in those cases it can be boarded out, and it is very powerful in other grindy matchups. I might try the new Karn in this spot, but have not tested him yet.
Lands: 25 and not going below. I think this is already quite greedy, and sometimes I cut a Factory, Wasteland and Urborg in order to play 16 basic Swamps. Getting mana screwed with one Swamp and lots of double black cards is a surefire way to lose, and happens frequently.
The rest of the deck is almost a quad laser, courtesy of missing deck manipulation and my personal need for consistency.
Where do I think Pox stands right now? All in all I think we are situated quite well, with several good matchups and a few abysmal ones. I really struggle with NicFit, TurboDepths and Burn, Lands also feels like an uphill battle. Miracles is hairy, but if feels worse than it actually is. I would say 45/55 in Miracles favour. Most combo and cantrippy blue decks are favourable for Pox. Big Red is so/so, I win some matches and lose some, not quite sure on this one yet. Bridges can be a beating, as we almost can't get rid of Walkers without the attack phase.

