As part of Comic-Con@Home 2020, Magic: the Gathering head designer Mark Rosewater held a one-man virtual panel to talk about the future of Magic, specifically about the upcoming Zendikar Rising set. He wasn't able to offer many specific details, but he did discuss some high-level themes, and offered a handful of teases as well.
One of the core concepts behind Zendikar Rising dates back to 2003, when Rosewater first became head designer. Back then, one of the ideas that he was very passionate about was land-based mechanics, which eventually led to the Landfall mechanic that was featured in the original Zendikar set. The new set will once again be a "land set", featuring the full-art lands that all Zendikar sets are known for. The set will also feature six dual lands that Rosewater has been "very proud of", and he is excited that players will be able to use them. Zendikar Rising introduces a new mechanic, which Rosewater describes as a popular mechanic with a new spin on it, but declined to go into more detail. There will also be two returning Zendikar mechanics, as well as three returning planeswalkers.
The panel also unveiled a new kind of booster pack, which is called a "set booster"; this is an entirely new form of booster pack that will not be replacing any existing products. Set booster packs are designed to be "fun to open", as opposed to draft boosters, which are specifically designed to be used in gameplay immediately upon being opened. Wizards of the Coast determined that over 50% of booster packs are opened and inserted straight into a player's collection, and these set boosters are targeted toward these players. While draft boosters have one "excitement point" (seeing the rare/mythic rare card), set boosters are meant to have multiple excitement points.
Each set booster will have twelve Magic cards and two "Magic-related" cards. The first card is an art card, with 5% of these cards having the artist's signature embossed on the card. The second slot is a land card, which will be a full-art land for Zendikar Rising; 15% of these will be foil cards. The next six cards are "connected commons and uncommons", where all of the cards share some sort of thematic or gameplay similarity; at least one card will be uncommon, though up to all six of them may be uncommon. The ninth card is the "head turner" card, a common or uncommon which is either a showcase card or a card of another type that Rosewater declined to elaborate on. The tenth and eleventh cards can be any level of rarity. The twelfth card is the standard rare/mythic rare card, and the thirteenth card is always a foil card of some rarity level. The final card is an ad or token card, though 25% of the time this will be a card from "The List", a list of historic Magic cards that will be presented exactly as they originally were upon release. Ultimately, players could receive up to four rare/mythic rare cards in a single pack; Rosewater stressed that while set boosters are more expensive than draft boosters, players can expect roughly the sane number of rare/mythic rare cards per dollar spent.
If you're interested in hearing more of the impetus behind the design of Zendikar Rising or set boosters, or if you want to see the card art that was shown on the screen, you can watch the recorded video of the panel below.
Rosewater followed up with an article about set boosters, which includes more detail on things like rarity percentages; you can read that article here.