Wait a second! Pausing at 0:25 showed me the high slots actually have the high slot icon (3 lines, instead of 2). Could this mean medium stuff is incoming?

Unlikely with respect to the dropsuit stuff. Having a substantially different dropsuit fitting screen isn't something they'd do "just for show". The only people who'd notice it is different are people who've played Dust. Everyone else will see it and not have much idea what it is beyond some kind of configuration screen.

The additional of a M slot for weapons, the removal of the grenade slot, and the conversion of the High module slot icon to be the same as EVE, with the three lines instead of two lines, are all fairly significant changes. They have no artistic basis, either.

This wouldn't be the first time we've gotten a preview of aspects of a forthcoming build from promotional stuff CCP has done. For example, we got to see female dropsuits for the first time during that Chinese game show a few months back, whatever it was called. As all of the changes we see in the dropsuit screen are changes that make sense to me, I'm more inclined to believe they're indicative of a broader change to how dropsuits will be configured, rather than arbitrary changes CCP made because they figure people seeing two seconds of a starter assault suit with two Low module slots rather than one would be really awesome.

If you're familiar with EVE, you should know that CCP's game trailers lie. Their EVE trailers are always spiffed up to look cool, when a ton of the stuff shown isn't actually in the game, doesn't work how the video shows, or has significantly better graphical effects than the actual in-game. It's something a lot of people have criticized over the years. They're meant to attract new players and look awesome, but in general, aren't very accurate to how things really are.