I just found another Hamburg press preview from Voyger532 of the German Ubi forum.
Key elements from the preview (things we didn't already know)
- Ships do infact have crew walking around on decks. Confirmed

(But they still walk around acting like nothing has happened while a ship is sinking, hopefully this will be dealt with)
- You can actually identify which rooms of a ship have been hit in the torpedo holes
- Some ships, not all, do jettison lifeboats (no, he didn't try shooting at them)
- Enemy fire actually makes physical holes in your own hull too. (You can still dive, and water wont rush in... hopefully also will be worked on)
- Direct Translation: The Damage management has been completely overhauled. It used to be that a part was damaged, with the time to repair completion shown. There was something like a difference between a minute to repair, or not at all, because it was destroyed. Now (in SH4) every system of the sub has a coloured bar with the degree to which it is damaged next to it.
- The measurements used in the demo were all metric. (Hasn't the option for imperial already been confimed?)
- On the multiplayer demonstration: The player stands on the bridge of a destoyer, and controls the entire lot of convoy escorts. You can give the other escorts commands via the map. He's not sure if you can switch between ships.
***LAN - 1 escort controller, 7 subs... Internet 1:3
According to Emil Gheorge:
- There will be resupplies at sea
- There will be new mission objectives given out by radio, but general radio traffic has also been doubled
- There is still a point based reknown system
- An improved version of the mission editor will be included
- If sales are good, there might be a destroyer command
- They haven't even started thinking about an SH5 yet
- Unfortunately there will be no abandon ship feature
- You will be able to tally the depth charges from a destroyer to count how many he has left. (no idea if this refers to an inbuilt tally feature)
- No Dolphins

But plankton, algae and rocks are there.
- Sun and moon movements are apparently 100% correct for any given day.
- There will be a simplified thermal layer system
- SH4 will be as moddable as SH3, but extra models can't be implemented!!! What the Hell? (But didn't we also think this in the early days of SH3?)
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EDIT: More info from an Emil Gheorge interview in Hamburg by the 9te Flottille added.