While hardly a staple in Modern, Domri does see tons of play in Commander. This is especially the case in creature-heavy decks led by Commanders such as Xenagos, God of Revels, Animar, Soul of Elements, Surrak Dragonclaw, Mayael the Anima, and many more. There’s plenty of demand for the Gruul-colored planeswalker from the EDH crowd and he’s sought after by casual players, as well.
Domri isn’t a big player in Modern right now, but he’s definitely playable in the format. There is one deck in Modern called Domri Zoo that is primarily a Bloodbraid Elf aggro deck, but plays one copy of Domri Rade. That's partly because he's a 3 mana planeswalker, so he's a great target to hit with Bloodbraid Elf's cascade ability. Who doesn't want to cast a Bloodbraid Elf into a Domri Rade?
In a creature-heavy deck, Domri's +1 loyalty ability can essentially draw you a card by putting a creature in your hand - although he can whiff. His -2 is a form of removal that’s decent enough if you control a creature larger than the one that you’re fighting (unless you’re playing creatures with Undying or Persist). Domri’s emblem is quite good, but in a fast-moving competitive format like Modern, it’s rare that Domri will ever get to 7 counters.
While he may not be a card with a high price tag, Domri Rade is still a decent mythic rare to pull from a Modern Masters 2017 pack. He could reemerge in the format if Domri Zoo or a similar deck becomes more prevalent in the format at some point in the future. Even if he doesn’t, Domri Rade is still a good planeswalker to have in your collection.