Made more progress, and I am a little disappointed in how the devs now seem to be forcing players to play the game in a certain manner.
The three main vehicles all have upgrades that permit them to reach greater depths.
The Seamoth has a starting max depth of 200 meters and an absolute max depth of 900 meters, which is coincidentally the bottom of the area known as the Lost River.
The Cyclops has a starting max depth of 500 meters and an absolute max depth of 1500 meters (last I checked), which is coincidentally just a little over the greatest depth that the Cyclops can hope to reach.
The Prawn has a starting max depth of 900 meters and an absolute max depth of 1700 meters (last I checked), which is coincidentally just a little over the greatest maximum depth of the game (1654 meters).
Each vehicle now has its own separate depth upgrades - previously the Seamoth and the Prawn could use the same module. The problem lies in the resources needed to build each upgrade. The Seamoth upgrade has easy-easy crafting requirements, while the Cyclops upgrade needs Rubies which can only be found at depths beyond 200m. The Prawn upgrade then ups that by requiring Nickel - and Nickel is only found in the Lost River, at depths between 500 and 900 meters. Note that this is only for building the upgrade - there's also the thing about upgrading the upgrade, for which you need a Modification Station - which can only be found at depths greater than 200 meters.
To upgrade the upgrades, the Seamoth now asks for Magnetite for the Mark II, and Rubies for the Mark III - both resources only found below 200 meters. The Cyclops asks for Nickel for its first upgrade, but then Kyanite for the final upgrade, while the Prawn only has one upgrade which also requires Kyanite - and Kyanite can only be found at depths greater than 900 meters AND requires the Prawn Drill Arm - so if you're one of the poor sods who's scoured the ocean floor and still haven't found two Prawn Drill Arm fragments, you're shit out of luck and need to keep looking.
Because without the maximum upgraded depth modules your Cyclops is not gonna travel deeper than the Lost River, and the Prawn will be unable to reach the deepest areas and you'll be stuck.
The thing is, while the Cyclops is a very powerful and very useful vehicle, it's also very large and very slow - two things that will work against you as you reach greater depths. Getting down to the Lost River will be a problem unless you find the "Cargo Entrance" (something I only first discovered existed yesterday) and it'll be a bother getting it down past the Lost River no matter how you look at it. This has led to people questioning the use of the Cyclops altogether - the Prawn in the hands of a clever player can do everything that's needed of a vehicle down in those depths - and during Early Access it was possible to do the Lost River and the areas beyond in one go, in the Prawn. Just plan ahead, pack carefully and activate the teleporters and you won't even have to worry about walking all the way back. If you make the journey to the bottom of the game in the Cyclops, you WILL have to pilot it up to the surface again eventually.
The new crafting recipes for the depth modules change this - now you're pretty much forced to max out the depth upgrade on one vehicle before you can even start using the next vehicle at depths past the default one. It's become a tiered progression that mandates that the Cyclops is included... unless you like making several return trips that were previously unneeded.
Clever? Maybe. Forced? Oh yes.
Oh, and a couple of new bits of info that could be useful:
# Eating a raw Bladderfish gets you some oxygen. No, I'm not kidding.
# Crabsquids can always find your Seamoth, no matter where you try to park it to prevent them from eating it. Turning off the lights doesn't do squat.
# Floaters are useless. There used to be a time when you could attach a bunch of them to unwanted critters and let (the absence of) gravity do the rest. Now you're lucky if you can get a Floater to stick to a critter, and far too many times the slightest twitch from the critter destroys the Floater.
# Because of how small, fast and accurate they are, Warpers are the only monster I see a need to actively engage and stab with my knife until they warp out. You need about four stabs. Everything else I just steer clear of.
# When you find a large wreck (or lifepod) try to take the time to explore its immediate vicinity. Far too often Something of Note is located in the neighborhood, and far too often in a straight compass direction from the wreck.
# Check every side of a wreck carefully, in at least two cases you can enter a "locked" wreck (one where you need the laser cutter) via the air ducts.