-I read there are some concerns long term with the NS keybeds (can't remember which model). Is this accurate for long time users?
-The things keeping me away from getting it, are: not having balanced outputs, outdated USB (no midi/audio) and to connect additional devices. Lastly the low memory for samples, and the fact that it seems Nord didn't really care about all these, even though there were a problem for a long time now.
-Out of the all sections, the synt interest me the most, next the organ.
I'm not sure how different the 73 key bed is from the 88 apart from the 15 keys, but I've had my NS488 for 2+ years and have had no key bed issues. Then again, the keyboard is studio-bound and the longest trip it has made since delivery is from the box to a stand.
I agree with you on the skimpy memory for samples, but to be honest with myself, it's only because I am skittish about replacing anything already on the keyboard. I'm not actually a big fan of some of the factory programs, so if I were more willing to get rid of what I don't use, it may not be a problem. With some care and research you can find out what's not being used if you run out of available space. Given that we can buy non-volatile 1TB microSD cards to put in a smartphone and that even volatile RAM for run-time at the size/speed needed for keyboards is cheap, I just don't get why limitations on sample memory is even a thing on any instrument much less on a flagship $5K keyboard.
As for the USB, I think most are running these through an audio interface for sound quality reasons. Can you comment on why USB audio and balanced outputs are both in your wants list? Are you running really long audio outs in a noisy EM environment where balanced outs help, and if so, why is USB audio important? What additional devices are you speaking of? Controlling another midi keyboard or having another midi controller play layers of the Nord shouldn't be a problem.
If synth is high on your list, I'm not sure I'd call the NS4 the best in class. It feels very limited to me versus soft synths and synth-first offerings from other manufacturers. I'm doing sound design n soft synths then making them into samples if I want to play them on the Nord directly.