I really like the idea of a zombie deck, but it feels like the only good cards are at 3+ CMC and we have no way of pumping the zombies.
Black has pretty good removal, I feel like a good zombie deck might incorporate board wipes and plentiful removal in order to slow the game down. Zombie recursion provides card advantage in the long term but generally does not provide much short term benefit.
One older card which may gain value is
Cruel Revival.
I feel like zombie tribal has three problems, compared to something like Ally or Elf tribal,
1, no matter how slow the overall gameplay, or how much you forcibly slow it down, many zombies are 1 turn slower than that because they enter tapped.
2, there's a general lack of evasion, so the only real plan is sheer numbers.
3, they're doubly vulnerable since so much of the strategy is tokens, so many delay effects become elimination effects.
So maybe the questions to ask are....
Can you make a zombie deck without relying on token zombies? How would that look? I mean, if a card you'd otherwise play spits out tokens, that's a bonus, but I mean a typical mix of 20-odd creatures plus support spells. Certainly that leverages the graveyard abilities.
Can you do a general token deck where a significant amount of those tokens as zombies? Like mix in with other tokens for flexibility but leverage the right "count the zombies" abilities?