It's not about the bank itself dissapearing, that would at least have warning.
Its about do they remember to remind me to pay the extra five bucks a year? Do they take that five bucks automatically without me knowing it? If my current 3DS dies will I reliably be able to get back into my account? And "Do I really need to spend 5 bucks on this when it' does fit on the cartridge? What happens when it goes to the next console? Why is this service not just free with the damn game? Especially after having bought like 8 of them?"
Do I really care about this service for more time than what I already used it for to move shit forward once? DO I really want to bother doing that all again next time?
It was their coding in the first place that made trading between gens incompatible. Making the bank free for the first couple weeks was a decent gesture, but then you realize it was also their decision to make it literally impossible to get everything in XY without the old gens to begin with.
It's not about the whopping 5 bucks a year, (that's what, 41 cents a month?) its just the general feel and principle of the thing.
Some of those limitations are linked to the retarded Nintendo Network accounts, so yeah I assume if you lose your 3DS somehow you are screwed and you lose everything, the 5 bucks are most likely due to server maintenance, I've played games with subscriptions before so I don't have any problem.
The idea of this service is yes, to stay and be used as a way to transfer in future generations, it's currently working with 3 generations(well at least when the next one comes out).
I have 0 problems with the service, I'm glad they made it actually, I can restart my games, without having to transfer everything to another cartridge for example, that is a big plus for me.
And here I thought completing the whole Pokédex entries on Pokémon Platinum was a pain already.
Ever since the 4th gen it became pretty easy to do it, it's just timer consuming, with internet you can get all the rare stuff that was hard to get before.