This is probably a controversial opinion with those who've splashed out on one of them, but they essentially signed up for this to be e-waste as soon as it was no longer supported.
They might argue that the hardware is still perfectly capable, and I would agree, but this happens in other industries too, mobile phones, Sonos speakers, Wifi routers, and all sorts of other tech.
Anyone who buys anything that relies on the manufacturer's services to maintain the devices functionality signed up for this, whether they knew it or not.
In the home automation scene, many go out of their way to avoid devices with cloud services, or opt for devices with robust local APIs; those APIs may be removed at a later date, there is a real risk (See Google + Nest), but that's a risk they take.
I hope VanMoof, if necessary, will open up the local API, and given the money potentially available from owners, someone comes along and provides a suitable service, for a sustainable fee, which I assume buyers can afford, to maintain the functionality, and not relegate all of these bikes to the rubbish dump.