@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)