NOTE: I understand this may require a second thread, but I want to post musings here to point out some interesting synergies that are being missed by being straight BG
I think it may be more interested to use BUG; mostly because:
* Shardless agent allows you to guarantee Vengevine recursion (or nearly guarantee, depending on build;) If building around this synergy it may be hyper-reliable in the mid-game. It's noteworthy that the Buried Alive and Vengevine can't be hit by shardless, which seems like a plus.
*
Cavern Harpy (and if there are any other cards like it) can cast by themselves multiple times. Some of the supporting cards for Harpy in Aluren also allow you to bounce dudes back. This self-bounce seems like a natural way to get a 2-4 mana trigger for Vine
* Combining with the (now deprecated?) BUG Aluren deck may allow a two-sided win con. Insta-gib via fast aluren combo, or secondary win con of Mid-range aggro.
I know this isn't quite related to what you're doing; but the synergies of Shardless and Cavern Harpy seem too neat not to point out. It also addresses most issues brought up about bad MUs: Aluren combo can go off T3 easily if not interacted with; meaning you can race combo and out-value Miracles/Fair decks. This also opens up running FoW, which obviously helps slow opposing combo; making those bad MUs have that much more potential.
If I come up with a list that seems reasonable maybe I'll start a thread and then cross reference it here for anyone interested.
EDIT: It could also be considered as a sideboard plan to swap between a graveyard combo vs aluren combo