There are enough 3+ toughness creatures in THB that Im worried a 2/2 Haste wont be able to attack much, but there are enough artifacts that you should be fine playing Irreverent Revelers (especially in Sealed when theyll blow up Entrancing Lyre and Altar of the Pantheon)
Theres no news about seeing this treatment in a later set or in a Secret Lair tie-in, and the name cosmium is thematically tied to the plane of Ixalan, so I doubt itll be used again outside of a direct tie-in the Ixalan
White can draw cards from lifegain in various ways, but I personally shy away from Well of Lost Dreams and Dawn of Hope these days due to the heavy mana sink required to draw cards, and the inflexibility of when that mana is required
, and if you don't have it, you're spending a lot of on-field resources for a Link-4
Hop's Zacian ex's first attack, "Insta-Strike", only costs one energy, which makes it incredibly efficient if a player chooses to go second
This allows you to build up your board for an alpha strike (lethal combat phase), then deluge on a later turn to remove all of your opponent's defenses