I'd have to say no to player operable huge size ships, for a few reasons.
Firstly, what would they add? It's quite a lot of dev work to add in another landing pad type and the associated stations, yet as far as I can see all they would do is add power creep into the game.
Secondly, there's plenty of headroom still available on the large landing pads. People mention the Boa, which was roughly twice the capacity of the Anaconda in FFE, as requiring a huge landing pad; however, a ship the shape of an Anaconda that is scaled up to fit the size of a large landing pad would have roughly twice the internal volume of an Anaconda. More boxy ships (such as the Panther Clipper) would be able to fit even more onto a large landing pad. There's no point adding another size of ship when there's literally plenty of space on the large landing pad.
Thirdly, currently the economy of the game is completely borked, with credit earning completely out of whack with what things actually cost. To make matters worse, there's very little ongoing costs to running expensive ships, so in the end we are stuck with the biggest and highest-performing ships being basically the default option for those that want to get work done rather than being situational.
However, that all being said, I would very much be in favour of NPC only huge ships. They would bridge the massive gap between the little escorts/freighters that fly about and the megaships/capitals. If they were made to be more like an oversized regular ship, utilising standard modules (possibly multiples of them, such as different weapon batteries using separate distributors) and weapons, they would also be able to dip into the existing loadout variety without FD having to create vast numbers of specialised weapons and modules for them.