[Update #2]: MTG Arena devs have shared the Format Popularity Stats and their Plans for the Future.
[Update]: The Tales of Middle-earth expansion has now arrived, and unsurprisingly, it's quite flavorful!
After the success of two Dungeons & Dragons themed expansions, Wizards of the Coast has decided to get a little bit more ambitious with their crossovers. As such, on June 20th MTG Arena will be getting a full standalone set based on J.R.R. Tolkien's The Lord of the Rings!
The aptly named The Lord of the Rings: Tales of Middle-earth will be legal in the Alchemy and Historic formats, and it'll come with all of the same goodies as a 'normal' set. In other words, you can expect to see both draft and sealed formats, a lengthy Mastery Pass, a variety of cosmetic styles for the new cards, and more likely than not, a couple of themed events to mess around with as well.
Since Tales of Middle-earth is supposed to be an introductory set there aren't many new mechanics to talk about. The main one, and the one you'll be seeing in pretty much every deck, is "The Ring Tempts You". Whenever this happens you'll have to choose a creature as your Ring-bearer, as well as gain or upgrade The Ring emblem that will grant that creature certain powers (more on that in a second). You can get or upgrade your emblem without there being a creature on the board, though you can't have more than one Ring-bearer.
The Ring emblem gains its effects in sequential order and they all work together, and so a fully upgraded emblem will grant your Ring-bearer the following abilities:
1) Your Ring-bearer is legendary and can't be blocked by creatures with greater power.
2) Whenever your Ring-bearer attacks, draw a card, then discard a card.
3) Whenever your Ring-bearer becomes blocked by a creature, that creature's controller sacrifices it at the end of combat.
4) Whenever your Ring-bearer deals combat damage to a player, each opponent loses 3 life.
How all of this translates into actual cards, as well as what all of the other mechanics are even about, that you can check out through the freshly revealed card gallery. As for the accompanying Mastery Pass, you can find all of the details about it at a different corner of the MTG website.
Once the The Lord of the Rings: Tales of Middle-earth expansion goes live I'll make sure to let you know. Until then, have fun cooking up all sorts of new food decks!