I'm kind of over the "Liliana as Black Jace" fantasies - they're always 4 abilities, 2BB cost, and follow the same formula of +loyalty ability that's okay, -1 ability to kill things/protect self, -5 for something sickeningly powerful.
The Liliana posted above isn't that bad, although the +1 would have to be replaced, it's too broken.
I like the idea of a reanimation-based Liliana, along the lines of:
Liliana of the Veil - 1BBB
Planeswalker - Liliana
+2: Each player discards a card.
-3: Put target creature card in a graveyard to the battlefield under your control.
-9: You gain an emblem that says "Skip your draw step. At the beginning of your upkeep, you may pay X life. If you do draw X cards."
{3}
I like that it acts as a 1BBB Zombify which seems fairly costed, each ability relates to the other in that the plus ability feeds both the reanimation and mirrors the card drawing of the ultimate. The emblem is just based on an iconic black card, but it could be almost any iconic black card and still work.
I also like the idea of an 'Aggro' planeswalker in black that has a big loyalty boosting ability on a low casting cost, but the + ability only hurts you, no benefit.
e.g.:
Sorin on the Hunt - 1BB
Planeswalker - Sorin
+3: You lose 4 life.
-1: Something, possibly a removal-type spell.
-10: Target player gains an emblem that says "At the beginning of your upkeep, lose half your life rounded up."
{1}
As far as Innistrad Mechanics go, I think you're right about Threshhold not coming back (but you're slightly off about the reason; Threshhold didn't make people do things that didn't happen naturally, so much as it made them keep track of something they normally don't have to, because it can flicker things on and off constantly rather than triggering once when the card is cast, like Bloodthirst, so it can be marked and then ignored). I'd like to see Delve too, but I think it might be difficult to power-balance.
