Every deck in the format is capable of running Serum Powder. Why do so few choose to do so?
Because it's only useful if a) the exiled cards provide some ancillary value (castable creatures for example) b) your deck relies overwhelmingly on 1 and only 1 card and your deck doesn't rely on 1 or 2 of's to function that you can't afford to powder.
This is because the card Serum Powder itself once mulligans are resolved is a Bone Flute for the most part. If your hand includes Bazaar and Serum Powder it's largely irrelevant. So the reduced over all quality of a hand is marginal because a measure of a great hand and an unkeepable hand is simply whether it contains that ONE card.
Dredge is so far the only competitive deck in Vintage that meets that criteria. There have been Shop decks so bent on having Shop the opener they've played it. In Legacy an example of a deck that can use it is Leylines ... the deck needs 1 card in its opener, Opalescence. The Powder is moderately castable off Sanctum as well.