I look forward to reading it! While I think most of the simic cards fall short (the adapt mechanic leaves much to be desired), I like the idea of having a mono-blue dig spell. It seems that having a way to dig for a needed Lord or silver bullet like Mistcaller would be nice, especially a only a cost of 1 blue. Having a Rapid Hybridization stapled to it to deal with errant Wurmcoils or a Phoenix seems like a nice bonus, even if it cost three.

I have reservations about the new stifle too, although I could go the other way as well. Having a stifle on the play ready to hit an opponent’s fetch (all the while keeping up mana for a flashy Trickster) seems good, but perhaps that’s a dream that doesn’t come together as often as we’d like. However, catching O-Stone/Ugin wipes off guard seems like it should inspire us to at least consider it as a sideboard option. And the added clone benefit could make losing Reejerey more palatable for those (like me) who still stubbornly cling to him.

I’m actually discussing that card in depth next week. Short answer, no. You realistically never want Incubation and Phantasmal Image is better for cloning.

They don’t combine the way I think you’re thinking. Serum Powder happens during mulligans while Sphinx only triggers once you’ve kept your hand. You can’t Sphinx first, seeing if you want to keep the hand, then Powder it away if not up to standards.
Instead, you would Powder to find a keepable hand then Sphinx to get even deeper into your deck. This is certainly a very interesting possibility for combo decks, but I don’t think there’s a two card combo deck that could make use of this yet. If one does, yeah this could be incredibly broken.
That is true and it would be pretty decent were Chrome Mox Modern legal.

I can also see sphinx with chrome mox as a possible combo part.