Hm, manual and automatic refresh, yes thats something else to think about. Do you consider 40 cells to be a relatively good average size? If the display were cheaper, like 300$, 200$, or less, would you be more inclined to get one? Maybe thats a bit of a silly question, I mean who wouldn't want to get things cheaper? But what if it only had 30 cells? Or 20? Would a 100$ to 200$ drop in the bottom price be enough for half the number of cells?

Hm, interesting value proposition, it's seems a tricky subject considering individuals different needs, heh. I guess there would be a lower threshold for refresh rate, if only from an effective usability standpoint in term's of navigating or being able to properly read lines. What do you mean by timers, watches, and thermometers? Are you referring to more affordable versions, or different tactile models?

The 32 cell displays on allot of notetakers usually didn't feel too cramped for me, but I'd imagine that a 20 would.
40 is more ideal though.
IMO (slow) autorefresh is agonizing, and takes away much of the usefulness of a braille display.
I would much prefer manual.

Bluetooth isn't a must, but if you could pay like 50 bucks more for a model with it, than that would be great, since really, that's as much as you should have to pay at this point for decent Bluetooth (E.G. doesn't drop constantly or take for ever to scan slash pair) anyway.
With all the sub 150USD phones that have it, their just isn't any good excuse for it to cost so much outside of HQ audio or connection stability critical stuff like robotics; I'm not asking for multiple device profiles or switching on the fly either.
Same goes for physical memory or an SD card slot, things that are truthfully very useful for notes, but are often artificially overpriced.
I'd probably pay around 200USD extra for both things together, since you need firmware and batteries, and it means more things can go wrong, so if you offered repairs you may need more people or someone with more experience.
Speaking of batteries, I'd be fine with plain old double or triple A's on a wireless model to drive costs down if needed, they do it with mice right? :-)
As for the total, I'd really just hope for under 1000, since it seems foolish to try and go from 3K or so down to 500 in one go, and I insist on good build quality, both externally and internally; plus, maybe an included carrying case and cleaning kit, though I'd buy those things separately for like 60 and 25USD each as long as they were decent quality.

I haven't had a modern braille display for quite a long time though, mostly I'm going off my friend's experiences, so take my opinion for what that's worth.

I totally forgot about the Pie... LOL
Though I was under the impression that wireless mice and keyboards were quite reliable nowadays...

I also forgot to mention cursor routing buttons.
If the display is small enough for most people to read the entire thing comfortably with one hand, than I really don't see the point in paying for them, since unless something has changed, I don't think you can say, move your cursor to the start of the word and spellcheck it, and using left and right arrow keys to do so is fine by me.
Or are those really only a thing on notetakers anyway.

If it would truly bring the cost down than I guess I'd be fine with assembling it, but I don't think most people would spring for that. The option would be nice though.
Your still talking about tiny screws, reading through instructions, and perfectly centering small components, not losing any of them in the mean time, even without any soldering.
Unless you've done that kind of thing before, than you will be either pretty intimidated, or need a willing sighted person handy to help you (not exactly a confidence booster) plus they might just fuck it up not knowing enough about braille displays anyway.

As for case customization, I've never understood the appeal for most of that stuff, but I know several blind people who do, and I could see individual names (for differentiation) and or the name slash logo of the institution in braille being useful for larger orders.
Different case materials and styles may be useful too, for different price points and needs.
E.G. hard case with full protection, rugged  carabiner loop and optional waterproofing, larger soft case with padded shoulder strap and optional side pockets, case with adjustable stand, wrist rest, and small pockets, slim leather case with brass clasp, ETC.
Beyond the basic gray, dark blue, and black, I don't think much color choice would be necessary (for obvious reasons ) but you could see about the demand for it later on.

The pins thing well, I really couldn't say, it never even occurred to me to be honest. O.o
Their is always a trade off between overwhelming the customer with choices and allowing businesses (and some individuals) to customize units to their liking.
Ambutec is a good example of how to do it right, in my opinion.
If their are any true potential benefits to non standard pin shapes, than I would allow people to customize the main product, rather than choosing from multiple models, and I would have an easily accessible breakdown of the advantages of each choice available as well.
Otherwise it frankly just seems like a frivolity, though an admittedly pretty cool one. LOL