White card draw is a good guess. I wouldn't be surprised if that were it. Not sure how they would do so in a way that wouldn't be totally against the color pie. Maybe every time you gain life draw a card?
Something like
dawn of hope? That seems pretty terrible, but it would be so much better without the 2 mana requirement. Personally I don't like the condition of gaining life though. My first though was it had to be related to something white does consistently, and gaining life sure works, but drawing one card for each instance of life gain seems pretty lackluster in mono white. It would be great in Orzhov or something like Oloro, but they don't need that card draw. I guess this idea would work with mono white extort cards, but that is such a small population of white cards. I don't think a card that says "whenever you gain life, draw a card" would make
Basilica guards good in monowhite. And to have something that draws a card for each point of life gain is too much.
Then there is always the
mentor of the meek idea since white is known for their white weenies. Their Elspeth
soldier tokens, but again I don't like the mama cost associated with it It is just too much, but without a mana cost, it is too good.
Another thing white does pretty well is exiles stuff. A lot of it's removal is in the form of exiling.
Path to Exile,
Swords to Plowshares,
Crush Contraband,
return to dust, EVERY SINGLE
OBLIVION RING EFFECT! There are more examples such as rest in piece, I won't name them all. but what about an enchantment that reads something like "Whenever a spell or ability exiles a card an opponent controls, draw a card," or a sorcery that says, "Draw a card for each card your opponents own in
exile." I feel like this happens enough to get value from a card like this, but not enough to be game
breaking.
White isn't exactly known for its excess mana, or its card draw so adding the requirement of the former to gain the latter seems like a bad way to do things.