Personally, if it is not related to money, if I design oscilloscope it is not at all clear my selection for display aspect ratio is 16:9 horizontally.
The old architect told me at old days that the human eye is usually pleased with the Golden ratio. Also old photographist told same. I think everyone knows what a golden ratio is. In displays normal aspect ratios 16:10 is most nearly. (also used example in Siglent SDS6000 series. )
Analog scopes mostly have 5:4 ratio. Some times more. Reason was physical with some compromises also with tube manufacturing.
Modern displays, TFT etc do not have these same limits (Beam vertical deflection speed etc).
Modern oscilloscopes have many things what need more vertical room.
MSO example with 16 channels and simultaneously example 4 analog channels and simultaneously also digital bus data analyzing/serial decoding (perhaps multiple decoders simultaneously) also FFT when we still want look also signal in time axis or many other signals simultaneously with FFT or other math) Also including zoom window or multiple zoom windows.
16:9 display do not serve this well. Specially when we have signals with same time axis we need display these things vertically somehow separated but using same horizontal x axis. Also mostly we use measurements.
Simply, we need more vertical room. If we have multi window system we need big display and then we can move and arrange these windows how we like..
So why we have 16:9 (or other "wide" screen) horizontally mounted displays in oscilloscopes. I feel like it’s just drifted into like a driftwood, for no real compelling reason.
I think since most oscilloscopes, at least the lower end ones are 8 bit vertical resolution, a display with 480 vertical pixels is more than enough to display the waveform properly. I love 16:10 for computer monitors, and think it would be great for oscilloscopes too, but i think more important than the aspect ratio would be the resolution. It would be really nice to have 1080p displays on oscilloscopes, as with 1080 vertical pixels, you could display all 4 channels simultaneously, without overlapping the waveforms, and being able to see the 8 bits of each channel; and also, have the 1920 horizontal pixels would be nice to be able to see a longer time. If the displays were all limited to 800 horizontally, then yes, a taller aspect ratio would be nicer, but only because a taller aspect ratio would mean more pixels vertically.
Question is not about 8 bit vertical resolution. Of course 256 pixel is enough... but, example many Siglent oscilloscopes use 400pixel vertical range for waveform but it is also around 80% from ADC full scale. I did not even think ADC resolution behind my opinion what is based to over 50 year experience with oscilloscopes, in hobby of course and naturally including also professional use.
Old analog scopes have mostly 2 channels or 4 channels with single or dual time bases zoom/delayed etc...
We survive well with these and we make amazing things with these using mostly small display.
Who knows resolution...but Lot of more than 8bit, well I do not start talk about it, it have handled enough in film camera vs digital camera forums over years and years..
Today things are very very different.
Mostly today we have 4 analog channels.
Display have also lot of other information, whole meny system and so on.. automatic measurements with statistics, trends et.
We have 1, 2 - 4 Math traces, example 1 to 4 FFT traces and also with xt display same time available.
We have 16 digital channels (MSO)
Then we have 1 - 4 channels serial decode... many times we use zoom display
And so on.
Try look 4 analog channel, 1 - 16 digital channels, and 4 UART decode same time on display.
Or just example 4 FFT with 4 analog channels xt display
Measurements on, cursors on, measurement gate cursors on...
FFT harmonic peaks markers with data on
Also display need some main controls what you can use example with mouse or finger...
Lets then talk about 480 vertical pixels...
Reason is amount of things and information on screen, of course not ADC resolution what is still mostly 8 bit with 5 - 7.5 bit ENOB.
Vertical room is important because most of things have same horizontal axis. Just try 16 digital channels 4 analog channels and 2nd time scale aka time base in use. Yes rare case but, today oscilloscopes have and when they have they must also be usable. You do not miss more vertical room, no problem? I miss, and also I have old eyes so I can not see mosquito eye sized things.