Comparing this card to Delver is pretty errant. Delver ideally gets played on turn 1 and flips on turn 2-3 if you aren't @Brass-Man. This card isn't as aggressive as it takes time to build up the critical mass of instants and sorceries. And without the upside of a quick Delver flipping, you will have better things to do than playing a 1/1 on turn 1...like holding up a counter or cantripping to set up the card later down the road.
This card is functionally much more similar to Gurmag Angular and Tasigur than it is to Delver. A mana efficient mid-to-late game threat that has synergy with spell-heavy builds. Unlike the Delve creatures, it is in a better color, does not have the same diminishing returns, and evasion matters. The cons are that it will be slower as it doesn't have synergy with fetch lands and other card types in the graveyard, as well as requiring more overall mana.
I think the primary home will be in Legacy. As a starting point, take a Grixis Delver list, remove Black, and add Thought Scours to the cantrip package (obviously this is a rough draft):
For Vintage, the issue is the conflict with the delve spells, along with the issues others have brought up.
For Modern, it would take pretty significant metagame changes for this card to see play as Phoenix is more explosive and Dredge leads to significant graveyard hate. (Oh, and Gut Shot has made an unfortunate comeback...)
Just my rapid take.