I've been a TB member for.....oh.....2 days (?), and have only just ordered my first TB bag last night, but I thought I'd be in a decent position to give an objective opinion based on what see on your website. As I currently don't own a TB bag, I think I could be objective! Also, I have a lot of bags, and love bags of all sorts.
Aeronaut: A 35 litre size (similar to the Tri-Star), which may suit people who prefer the Tri-star's capacity, but want the Aeronaut's design. Keep in mind that the capacity of a maximum size wheeled carry-on suitcase is roughly 30 litres. A 35 litre Aeronaut wouldn't be considered small in terms of volume. In fact, such a bag would fit more stuff, and yet be physically smaller than the typical wheeled carry-on. Win-win! It would also be easier to carry than the current Aeronaut.
This will sound quite anecdotal, but last summer, I travelled to Prague (and other parts of Europe) for a conference with my wheeled carry-on suitcase for 2 weeks. I packed a whole bunch (7 or 8) t-shirts, 3 pairs of shorts, a pair of jeans, a business shirt and trousers, and even a pad of paper and some printouts. I never washed My suitcase was only 27 litres, and was large enough for all of that. Yes, I had to check it in because my 15 year old carry-on was a Samsonite tank that weighs ~5 kg, but imagine having a lighter Aeronaut to swallow that up!? I'd still have room to spare.
Tri-Star: I'm a fan of compartmentalisation to keep things organised, which is why I love its external front pockets so much! However, I don't like it when bags try to be too organised because I feel that while the total volume may be sufficient, the space is only accessible in bite-sized pieces.
Could we see a "Duo-Star" with the same capacity? That way, you get a deeper compartment for clothes, and still have a laptop compartment for a laptop and cables. Also, since "ultrabook" laptops have become increasingly common, perhaps the laptop compartment could be made narrower. Nowadays, even a 1" laptop is considered thick. If the laptop compartment was narrower, and padded compartment so that a laptop sleeve wasn't necessary, it would be amazing. Do people who can afford a Tri-Star still carry 1.5 - 2" thick laptops?
Messenger bags (in general): Personally, I like using messenger-style bags, whether it's a proper messenger bag, or a "man-purse"/satchel. However, I believe that the top flap on most messenger-style bags is too tall. If the bag is hanging on your side, and you want to access something, you need to open up the flap. Since the flap is so tall, the flap gets in your way! It reduces visibility, and generally makes it more difficult to reach into your bag. When the bag is open, the flap could reach as high up as your shoulder, or if it's a vertically-oriented laptop bag, then the flap may even reach your face!! Do people need flaps that long? Wouldn't it be easier to deal with a shorter flap?
Create a messenger bag with a 15-20 litre main section, add a thin padded laptop compartment (for modern, thin laptops), put the pockets from the Tri-Star or Western Flyer on the outside, add a shorter flap, and the result would be a fantastic messenger bag!
Thanks for reading. :)