The "fear" with ME is more that governments or someone like that could spy on us... (not really a "threat" to most people in Western Countries). But still better to get rid of it. Not an imminent threat per se.
This bug is a true security bug that has been lurking around for 10 years... and it could have been already abused. This is double scary because this attack does not leave any traces behind and it allows any application to pretty much enter God Mode (this is the worst case scenario of a security situation (hence the name meltdown (like nuklear meltdown is the worst case situation in a nuclear power plant)).
This bug is also bad because in certain situations the fix of this bug causes severe peformance penatlty.