Just started writing and didn't stop....
I think they are very motivated to pull it off or come very close to all four updates. The explosive success of the Valheim comes with additional expectations as well as business responsibilities & pressures that can be challenging to adjust to at first. I think the success has pros and cons in the short term but in the long term it should be overwhelmingly positive for the future of the Valheim and Iron Gate Studios. Assuming they are settling into the success, I think they'll have a lot of fun producing updates knowing the release of each is going to be played by millions of fans.
Right now, we are not even sure what Iron Gate considers an update worth titling or how far along they already were in these updates prior to the early release.
I'll speculate about the updates for fun.
Hearth & Home Update #1 | Speculation
I think the core systems of Hearth and Home are already in the game but it's possible that they have all new systems / crafting materials to figure out and balance which would take more time to develop & test. If new systems are limited, adding new building objects & furniture is probably relatively easy & fun compared to when they were figuring everything out for the first time.
New content for this update could be mainly about having a good & distinct idea for a new object or building part. Then it's modeling, texturing and ultimately making sure it makes enough sense to take up a slot. Depending on the object, they may also need to stress or exploit test. My guess is that the majority of the update is modeling, texturing and a smaller portion is new code / systems which means the code developer is free to work on other updates. I would be pleasantly surprised if we see all new building / interaction mechanics coming with Hearth & Home update but think this update could rely more heavily on the model/texture artist.
Cult of the Wolf Update #2 | Speculation
I'm not sure what this is but it sure sounds fun / dangerous. My guess is it's a combination of new camps/destinations, humaniods? living or ancient history plus lore and my hope is that our interactions with tamed wolves is somehow impacted. Without knowing what the update actually is, it's hard to gauge what type of work (Coding, Modeling, Texturing, Sounds, etc.) is required to accomplish it. I think this one will require talents from the entire team. Adds to existing Mountain / Black Forest Biomes.
Ships and the Sea Update #3 => Saga Worthy Seas, even more ships | Speculation
For some reason this one is most interesting to me. I think it's because I love the sailing mechanics in the game already and don't know what other ships we even need and for what reasons. Maybe their will be enemy ships / ocean dwellers. Either way, I think it's exciting for the number of unknown directions they could take it from more water mobs, island destinations?, deep sea fishing, reasons to swim or maybe dive (treasure), weather effects like cyclones? Ultimately, the update could be small or large and be an update that gets released this year.
Voyage to the Mistlands Update #4
I'd speculate that out of the 4 updates, this one has a solid plan and probably already has content that is being tested but has many parts that must all come together. It's the most important to get "right" the first time in terms of being distinct, complete and a balanced logical progression to the game. I'm very curious at how they will add more Biomes and what each will bring. I suspect this update is their personal goal for the year and hope they accomplish it!
If Odin wills it
My feel is that these are less about goals this year and more about when they find the time and will to squeeze these wish list items between the other titled updates this year or the next. I think when they are added is probably more dependent on whether the other updates steer them into these areas or even as "breaks" from working on the other updates. For example, Moon Phases... I can see that tying into Cult of the Wolf. Expanded Trader inventory with the Sea / Ship update + random fun ideas that the team has for "mini-games" and quality of life enhancements.
All in all, I think they know what they are doing and have every intention of releasing as many update(s) as they can provided it meets their own & community expectations and quality standards. I really like that they went back and revised the Troll and two Bosses. It's less about whether they needed a revision and more about what that says about their development process and personal standards. I like it.
Road maps can be ambitious to motivate themselves as much as hype the community and development usually does take more time than estimates. Not everything goes to plan and priorities change all the time.