My main concern here would be gameplay balance related (something I find to be shaky at best presently between the 3 Ships we have and may be due for an overhaul to reasses some things based on changes that have happened with gameplay over time). That is to say they are roughly based around:
(Small) Sloop = Nimble, Shallow, Fast Reaction, Combat Weak, Fastest in Headwind, Balanced around 2 Crew
(Medium) Brig = Lumbering, Shallow, Moderate Reaction, Moderate Combat, Fastest in Crosswind, Balanced around 3 Crew
(Large) Galleon = Lumbering, Deep, Slow Reaction, Combat Strong, Fastest Tailwind, Balanced around 4 Crew
And that...is about the lengths of the areas that things are balanced around. It is admittedly a bit more complex than that, but these are the primary points at a broad perspective level (you can get fairly granular on some of those categories, much less so on others). As such, I am hard pressed to see where another Ship Class falls in here. I can see make additional Ships that are variants in some way of the existing Classes by having some modifications to layout and horizon profile, though even this I see being a stretch to make sure all the existing Cosmetics work with this kind of thing.
Also, bumping the Galleon up to 5 players would just be a bit too much. I don't think the largest Ship potentially on the Map should be able to have any more than double the Crew of what will likely be the smallest Ship on the Map in any given server (from a perspective based around what these Ships are Balanced for in regards to Crew size, as going with less than a full Crew on any Ship is asking for things to be harder, and I say this as a solo primary). That is already a tall order for many people to deal with, so knowing there could be someone out there with more than that is just daunting.
Now, that all said, I don't think your opinion is unpopular really. A lot of people would love to have larger Crews to play with more friends, and I'm sure no one would actually complain about having more Ship types to choose from. It is more just concern about how to make that all work from a gameplay perspective that doesn't potentially damage the precarious balance that the game has (and probably could stand to have a step back taken, looking at the whole of what the game has become, and then reassess some of the balancing factors a bit to get things more in line again to what we had at launch - just with more content in play). Even with that, though, I would still be hard pressed to try and slot anything else in that wasn't essentially just a cosmetic variation of the existing Ship classes.