More windows is probably a good call. I love how you incorporate the signature Rhineland circular elements. Maybe consider having a vertical circular window for a multilevel lounge space, the way that the Dorado shuttle has it's exposed central area? It would be distinctly rheinland while also being uniquely a pleasure craft. Of course, I'm sure you have already thought of a million reasons why that would be far more difficult to implement than it is to suggest!
I'd think about adding some curves. Allows more internal capacity and gives you room to make some fine embellishments as the other liners have to mark their "luxury" aesthetic. Don't be afraid to stretch it out, either, the bridge portion and engine sections of existing liners are quite small in comparison to the rest of the ships. The Elbe does a good job of taking the Rheinland look and making it larger, less blocky, and more attractive to look at (since let's face it, that's why we fly liners in the first place).
I like it and i had the exact same thoughts that i found in the comments after looking at this nice model. More Windows at the flank in the middle/belly for the passengers, and a bit wider would make space to fit luxery inside and disminue the agressive/military look just a bit. And it may would get a even better harmony with the thick bellyfins.
I was expecting the first Rheinland lux liner to have the front or the back to look like the civ liner with the other end going for more of a Rheinlandish look. First look at it (not having a ship next to it to compare its size), I thought it was a fighter maybe gunboat. And the pointy thing in front, doesn't do it for me.
It's a good attempt, better than what most of us can do that's for sure!!!
I like the fins on the side. Rheinlands version of (I could be wrong) of the Atlantis look.
I would say make it wider like the other liners. More windows as well. Maybe take the Elbe as a reference with a civ liner.