With it being so briefly described so far, we could easily
each have an idea of what it should look like and each be different though (and everyone’s guesses could be proved wrong if later one is described in the HH books). Are you seeing this as a particular commission for you personally CAL001, or is O-man hoping to produce a Stormbird model for more general sale? I know you suggested it, but, if the latter, could people generally not have input and more of a consensus look be made? (if consensus be possible on such a thing!) If a good looking Stormbird could be made I’d love to buy one(s), it’s just a tricky thing to do justice to and I'd just want it to be done well.
My favourite of the models, drawings and computer images from this thread so far is the Deviant Art one, mostly because it’s the only one that actually
looks like a Space Marine design of vehicle,
however it doesn’t really look like that much like a Stormbird – where are the wings that can sweep forward in a hawk like sort of way? Also the vaguely BFG-esque front pram is weird too – it should have a cone nose, the lower part of which could come downwards as a ramp IMO. They’ve very much kept and changed the wrong bits of SM aircraft design.
I’m really not a fan of the look of the old VTOL Ultramarines dropship – it doesn’t fit the Stormbird’s description or look anything like any current Space Marine craft (I know it’s an older design but still...), if you loose the VTOL bits – which should definitely go for a Stormbird – which take up a lot of the art, then with the perspective you’re really not left with much to go on anyway and I don’t think the graffitied nose, rear fins or ramp are anything to write home about. I reckon starting from scratch, with the description and borrowed design tropes from other modern SM flyers would be better IMO.
I like some features of Warmaster Nice’s model and sketched one, but overall don’t think the design is how it should be done (sorry WMN!) – your sketch in particular looks like a modern day plane, not a SM void/air capable craft. I’m also particularly not liking the idea of having that angular crate thing below to carry – IMO it should be a big sleeker craft that carries its troops/vehicles inside its main body. To be fair as a conversion/scratch build it’s great and thumbs up to you for making it! It’s not what I think a designed Stormbird should ideally look like.
Hmmm... I wonder if I could ask my friend - who’s on good terms with Dan Abnett - to ask him what they look like, or possibly if there’s ever any chance of a slightly more detailed description ver popping up (without fully saying what it was for). Not sure if I’d want to ask my friend though, or he’d want to ask Dan, or if we’d get a response.
My personal my vague off-hand musings and ideas for what it could look like would be a little more hawk/bird-like, sort of. As in a sleek, vaguely cylindricalish, centre section, that could open either end. Then with two massive high up wings coming from the middle to the middle-of-the-back of the craft, sleek and curved and vaguely birdesque and which, when looking down on the vehicle when swept forward in flight, would look a little bird-like in profile, or in some way. Googled up a not that great quality picture of a hawk on the internets, which
sort of illustrates what I mean,
though not all that well - I was imaging wings rotated rather more forward than that and also somewhat less deep, but it was the best I could find.

Phew... too long a post! I can has waffle.