What I'm reading from <https://ninjalab.io/eucleak/> is this:
>This vulnerability – that went unnoticed for 14 years and about 80 highest-level Common Criteria certification evaluations – is due to a non constant-time modular inversion.
The vulnerability is therefore that the secrets can be extracted without taking the YubiKey apart, by measuring timings, thus tricking you into thinking that your YubiKey is intact (but you were already compromised the moment you could not account for the location of the YubiKey). On the other hand, a well motivated adversary can take apart your YubiKey, extract the secrets through other means (every hardware key is vulnerable to this) and finally put together a new YubiKey, identical on the outside to your old YubiKey, with the same secrets.
The two scenarios are almost the same, unless you're biotagging your YubiKey (which only buys you knowledge that you've been compromised). If Yubico is selling these keys, it's because it would be too expensive for them to clearly label the firmware version on each YubiKey sold, for various reasons. I think this is a great opportunity for a competitor to arise, who hopefully allows flashing of the firmware, at a minimum. The Nitrokey seems like a good option <https://www.nitrokey.com/>.