IF you could meld VARIOUS cards instead of just two specific ones then i could see it becoming a more useful archetype. Think about it this way; ANY devil/demon creature (+) a plant or treefolk could give you a elemental horror. It could be a mechanic called "Possession", where taking creatures of a certain type could meld from your field, suspend the card of choice from your hand and then bring it into play a turn or two later. The more creatures you use the less time you have to wait. Or you could just pay a large mana cost to play the creature directly. This would be cool to see if wizards ever tries that. It'll be mixing multiple mechanics but you're taking away the
weakness of one by adding the speed or strength from another.
Aldo for the Liliana build I like the W/B idea but don't you think that you'd get more play ability if you added BLUE instead of RED? Or maybe even GREEN if you want to use
second harvest? Now if you're going for the aggro feel then
stensia masquerade combo with
graf harvest will be a nasty combo. As long as you keep your Zombies from getting board wiped you should be good.