Re: When do the lawsuits begin ? Class actions...
IANAL . but this is tricky to argue I think.
If anything it's the SW vendor that you sue, they are creating the performance degradation. If there is some intel documentation stating that it is guaranteed to be secure, then yes a lawsuit would have potential.
Intel instead would argue that the pre-KPTI implementation is a performance feature and does not guarantee security, and that SW should use a KPTI like implementation if security is to be improved. They will also not promise KPTI is secure either. This fits with the Intel PR blurb that stuff is working as expected.
And SW vendors sell SW on an as-is basis - for eg you cannot sue them for any patches/bugs.
Neither Intel nor the SW vendors promised anything here.. it's caveat emptor. So unless you can prove your evaluation of the processor and/or SW was affected by misleading statements from these vendors, the products are not sold guaranteeing security.
So the court could rule that how you evaluated whether it was fit for your purpose was what was flawed.