UPDATE: Bethesda confirms Fallout 76's seasonal battle pass-style system will remain free for everyone.
You can often tell how well a live game is doing based on its updates--frequency, radical changes etc. If a GaaS title is constantly shifting things around and trying new things, odds are it's not monetizing well and the devs are trying new tricks to see what works. That's apparently happening with Fallout 76 and Bethesda's aggressive push towards new models.

Fallout 76 has pretty much tried every popular monetization scheme under the sun. Now it's trying something new, well not new for the industry, but new for the game. In an attempt to re-engage its playerbase and spin the Engagement Cycle wheel, Fallout 76 now has a tiered progression system right out of a battle pass. This system is free at the start, but Bethesda inadvertently hints we may have to pay for battle passes eventually:
"You will be able to take part in our inaugural Summer Season for free as soon as it begins with Update 20. All players will have full access to a single unified progression path, which means everyone is working towards the same rewards through the entire season."

Why mention the free aspect, or the unified progression path system, if gamers didn't have to eventually pay for it? Bethesda seems to hint there will be two forking paths: a free version, and a paid version, thus forking the community. I hope this isn't the case. Fallout 76 will be incredibly over-monetized if this happens.
Here's how it works: As you complete challenges, the game will no longer reward you with Atoms. Instead you move along a stylized game board to unlock goods like weapons and other goodies. Every square represents a new rank unlock, straight out of a battle pass system, and as you level up the unlocks get better and better. The seasons will run for 10 weeks

The main goal here is to incrementally give players rewards and feed them tidbits of content and unlockables as they play. It's a way to speed and beef up the critical Progression aspect, or #3 tier on the Engagement Cycle. It could work, but only if the game is scaled to dole out realistic rewards for the time investment.
It's also worth mentioning gamers can spend Atoms to unlock ranks two weeks after the season starts. So that means you can spend real money to breeze through the rankings (this is by design, of course, and offers a new way to incentivize monetization).
Here's all the things Fallout 76 has tried so far:
- Cosmetic-only microtransaction storefront
- mTX store updated with "convenience items" that allow you to pay to win
- 52-player battle royale mode via Nuclear Winter update
- Huge free expansions paid for by microtransactions (Wastelanders, etc)
- Fallout 1st, a monthly subscription service that unlocks private worlds and more
- Re-release on Steam
- Battle pass-style progression scheme
So what's next? Fallout 76 going free-to-play?
Here's more info about the new battle-pass like seasonal ranking system:
As you complete challenges, the game will no longer reward you with Atoms. Instead you move along a stylized game boad to unlock goods like weapons
Players will see a new option on the Main Menu that will take them to a uniquely Fallout-themed seasonal progression screen. During Season 1, this will be a Captain Cosmos-themed boardgame!
All players begin at the first space on the board -- Rank 1 out of 100. Advancing along the board involves acquiring a new type of currency, S.C.O.R.E., obtainable through the revamped Challenge system and other in-game activities.
Challenges will be less complicated and easier to complete, typically involving activities players would complete by playing Fallout 76 as they normally would.
Rewards are handed out at every rank, with bigger rewards the more you advance and at specific milestones (Rank 25, 50, 76, etc).
Players will have the option to spend 150 Atoms to skip ranks after the first two weeks of a Season. After two weeks, players can move ahead in ranks by spending Atoms as a means for those late to a Season a chance to catch up.
Seasons will run for 10 weeks with a two-week break between the end of one season the start of the next.