An extensive post was made on thealong with a Youtube video featured below that would go to share what kind of content players can expect and the methods by which content will become available.
As you can see, Ubisoft intends to break the DLC planned over the next year into seasons, with 4 new maps and 8 new operators confirmed. These will come alongside game upgrades, updates, and balancing, as well as player skins. The developers are dedicated to keeping all of these things free with only entirely optional cosmetic items that must be bought.
The blog post explains a system by which all of this will work:
"While all maps and modes will be immediately available to all players, the new operators and weapon skins will need to be unlocked with Renown, which is earned while you play, or purchased with R6 Credits."
Renown is earned for everything you do in Rainbow Six Siege. Winning, losing, kills, assists, objectives, saving team mates, or even studying up on a tutorial video are a few things that will earn you Renown. Estimates from the developers expect that players will earn 1000 round per hour of play. Meanwhile, R6 Credits must be purchased with real currency and are sort of the fast track to just buying your way through the unlocks.
All operators can be unlocked with Renown. According to the post, unlocks will be relatively cheap and increasingly expensive. "the first one you unlock in each counter-terrorist unit costs 500 Renown," the post states. "The second is 1,000, and so on." Post launch DLC operators will cost 25,000 Renown, or essentially 25 hours of gameplay by the developer estimates.
Premium weapon skins will fall into the aforementioned cosmetic range of unlocks. Players will be able to purchase tier 1 weapon skins with Renown, but higher tier skins will only be unlockable with R6 Credits.
It's interesting to see how much infrastructure Ubisoft has in place to try to keep this game free to people who are turned off by microtransactions, and while the idea of a DLC character that must be unlocked by literally a full day's worth of actual gameplay, it's a novel attempt at keeping game-changing content out of our wallets.