Let's break it down:
Can a stuck inflator actually "happen suddenly" or "without any warning"? Practically speaking, no. At a minimum for it to be "stuck" it needs to be depressed... so it can only happen when you are activating it. This makes the amount of time underwater where one might encounter a stuck inflator exceedingly limited.
Does a stuck inflator "leave almost no time to react"? Well, if you are depressing the inflator you are by definition in the process of adjusting your buoyancy and should be very cognizant of what change you are making. There is no reason to have "no time to react" because you are already in the process of reacting to a buoyancy change at that time.
Sudden difficulty accessing your dump valve? Such as... ? Again, that's a different problem. Would suck if you had a stuck inflator valve while you were experiencing whatever additional problem is currently making it difficult to access your dump valve. Figure out what problem THAT is... and fix it.
Trapped air? That's another distinctly separate issue from a stuck inflator hose. To build on what Rich K says above, two nuisances = 1 problem. If your wing/suit traps air and cant be vented properly... fix that issue. This way, if you ever have a stuck inflator... it will only be a nuisance and not a problem. Also keep in mind, that since you'll almost certainly be in the process of adjusting your buoyancy if/when you experience a stuck inflator... would you be venting and adding air at the same time? A little bit of stuck air - whether due to a gear issue or diver orientation - shouldn't be a problem. If you've got a lot of air already in your wing (trapped or not) while you're in the process of ADDING more air, perhaps you're overweighted?
Ultimately, what are potential causes of a stuck inflator hose? Typically it's either poor maintenance (gear not being rinsed, stored, serviced in an appropriate/timely fashion) or a piece of debris such as sand getting lodged in the mechanism. Proper gear maintenance, service, and pre-dive checks will virtually eliminate the first set of issues. Even a slowly leaking, rather than "stuck" inflator can be identified and corrected during the most rudimentary pre-dive check. The second can be largely prevented by taking care where and how your gear is placed before and during a dive. Don't throw it on the ground, drag it through the parking lot, or crawl around on the bottom and the likelihood of debris causing your inflator to stick approaches zero.
I suppose that theoretically speaking your inflator could produce a run-away inflation if you experienced a free-flowing first stage, but with downstream demand valves in both your primary and backup regs that's where all the air from a free-flowing first stage would go.
Long way of saying... don't put major focus on what little things might happen. But do put a little focus on things that can help ensure that nothing major ever does happen.
Yup, that's why I didn't say "easy to find" or that they can "universally be found" but either way I don't think I'd put an undetectably slow leak in the "emergency situation" category.
No ice diving... but plenty of cold NJ diving. Never had that problem. Is it common to occur in that setting other than when the inflator is being actuated... ie "suddenly and without warning?"
That said... if it goes along with the environment it is something to be considered during the dive plan, equipment check, and to be on guard for during the dive. Accordingly it should not "happen suddenly and without warning" unless you jumped through a hole in the ice with the assumption that the water is 85F.
Ray, I think you are arguing with a whole bunch of things I have not said... which I accept as my fault for not being sufficiently explicit.
I was comparing stuck inflator to, for example, running OOA. I am not really concerned about running OOA since I dive doubles, I monitor my gas, I can see it depleting, I know my consumption rate, and I would have to fall asleep on a dive for it to suddenly run out unless something freeflows, in which case I shutdown my valves, something I regularly practice... knowing it used to be an issue for me, now on every dive I try to periodically wiggle each of my valves at least once or twice during a dive to convince myself that I can still do it, and to build muscle memory, so it gets more seamless over time... I am not not worried about running OOA, even if it constitutes something of an emergency, because I am prepared equipment-wise, training-wise, and through regular practice, to make it a low-probability event.
I depress my inflator and deflator without thinking... so no, if it started freeflowing, it would not be happening at a time when I am fully alert and focused on my inflator, and potentially expecting such a problem to happen. I thought the whole point of building muscle memory is for things like this not to occupy your mental bandwidth. So, unlike the OOA situation that comes with a "progress bar", I would consider this rather sudden and unexpected. And, I don't do any stuck inflator drills. Maybe I should.
Of course, diligent maintenance will minimize the risk of this happening (I do flush my inflator and deflator after every dive). But, the same argument can be made for any other issue... I think the point here is that, knowing a stuck inflator to be potentially a fast-evolving event helps to realize that we need to pay more attention to that piece of equipment to make sure it is really low risk.
Anyhow, I never claimed that stuck inflator in and by itself represents an emergency. I do think it creates a potential for a problem that comes with a bit of a time pressure, and time pressure creates a potential for mistakes, so I will take such a risk seriously, however small you might think it might be.
Most other points have been addressed by others... as for having difficulty dumping, my sidemount rig came with only a single dump valve, with a dangling cord that gets entangles with a left chest D-ring. The weight pockets on my sidemount rig also tend to cause air trapping when loaded with larger weights. There are small fixed I made to make things better, but ultimately, I just had to expect it and learn to deal with it. The rig was designed by famous cave divers, and yet, it comes with what I find in practice to be considerable design flaws.. apparently, contrary to what you seem to be implying in your argument, you cannot avoid all problems by being diligent.