Coalition Relic is one of those cards that went from worthless to gold as Commander (then EDH) gained popularity years ago. When it was reprinted in Dual Decks: Phyrexia vs. The Coalition it took a significant hit, though it has creeped back up in value since that release. With the release of the four color Commander decks, I would expect to see an uptick in demand.
Supply is quite low online right now, and I would recommend picking up a copy of the Commander/Cube staple now if you need one. It's unlikely that the card will be reprinted any time soon, and I expect it to see more gains in the near future. Commander 2016 was the most realistic place for a reprint, and it was Chromatic Lantern that got the nod in its place.
The spread on Coalition Relic is still around 30%, which doesn't make it a slam dunk, though buylist prices have recently increased from $5 to over $6. I can think of worse cards to buy a set or two of.