@moorebrother1 it is not that unusual that during the release of a new (hyped) standard set, prices of eternal cards are declining. Players getting out of their expensive staples to buy into drafting/the new standard meta. That + the EV of treasure chests and changing drop rates of those staples I think are more of a reason for the current prices then the whole arena debate (the price of standard on mtgo isn't that low at all).
collections on mtgo will probably decline in the mid to long term due to arena, but before that i think we might see rising prices on those staples again, for example when modern is the talk of the town again in spring. (excuse my bad english!)
@ChubbyRain I really like the second idea (top end of a xeroxy shell) a lot, because as stated, you don't need to warp your deck around the combo to work. It rather provides xerox/bug decks a second path to victory without deluding its main game plan too much (if at all).
In a way, rather than the doomsday approach, it functions somewhat more like a vaultkey splash – with different mana requirements and slightly more expensive in total, but without the need to put dead cards in the deck.
Moreover, both combo cards developing the game state/providing utility on their own – is there another 2card combo that does this? From the top of my head, I can't think of one.
the 4cmc may be the one constraint, therefore Deathrite is a natural inclusion. And i like some number of Islands as @Macdeath mentioned. 2 Jace WoM seems about right, one doesn't want to draw too many copies of it i guess. And maybe even up to 4 jvp/snappy effects to mitigate accidentally discarding your good cards to Jace's +ability? Flashbacking a misstepped DC for the win seems good as well and snapcaster acting as a blocker to protect jace could be useful (another reason for deathrite, too).
Other than that, and with deathrite, DC and demonic tutor being the only black cards that are somewhat mandatory, the rest of such a deck may even be tuned to personal preferences/metagame expectations.
If the green splash isn't for you, maybe UB with vamp, hand disruption, fatal push and sth. like tasigur/angler is? Or Esper with mentor + plows, lavinia and maybe the new teferi? Maybe even transforming the currently popular ur/rug xerox deck to grixis?
Either way, the combo really seems playable, at least in a vacuum. The question is a) whether xerox/bug really needs such a new angle of attack and does the advantage outweigh the costs? And b) whether the new jace (being 4cmc and not able to protect itself) is good enough/fast enough, especially against aggro decks.
One more thing that might be relevant is the amount of tutorable cards you need to make demonic consultation wortwhile?
(not a native speaker, so sorry for any language errors)
I wondered if maybe Sun Titan could be a good Oath target in such a shell?
Depending on the game state it could get you both combo pieces with milled fastbond and/or crucible, it could find the missing part of the depths/stage combo (or any other land you need), it gets spheres to protect yourself/slow down the opponent, adds resiliency by returning destroyed/countered stuff if it stays on the battlefield long enough.
A split of expedition map/crop rotation might be worthwile then. And its trigger also plays around countermagic, it is semi-castable and one could even return stuff like oko or seal of primordium... but maybe all of that is just too cute