It's more a lore question. I'm sure that there is no restriction at all for domains and deities in the release version.
Knowledge (and Life) are seemingly domains related to Selune. Knowledge is also a domain of Mystra. I would have problems with this domain for Shar. If you take away the alignment good/evil and look at the funktion only (knowledge to do things, also evil things), I could justify also Light for Shadowheart, it's for blasting things away for the evil cause.
From the performance in the game, Light is probably not as good as Tempest (which has more lightning instead of fire damage), but clearly better than Trickery, from my EA experience. I cannot judge War, I think it's also stronger than Trickery. I presume that Larian will change Knowledge a lot from the DnD 5e version, so I have not the slightest clue about it.
Maybe I stay Trickery at first and then look how Shadowheart developes. Sigh.
