My understanding from a Google blog that talked about it indicated that Google felt like almost any speculative execution... is a risk. So while there might not be someone exploiting it now, they considered the practice potentially an issue. Accordingly future performance will possibly still degrade later as further changes are possibly needed?
Every company with high performance single thread designs has out-of-order with speculative execution designs, ARM, AMD, IBM POWER and mainframe/Z, Intel, MIPS, and SPARC. RISC-V is working on it, with the Berkeley Out-of-Order Machine (BOOM) and perhaps other cores.
And doing research I should have done a long time ago, SPARC V9 has Spectre vulnerabilities (https://www.zdnet.com/article/meltdown-spectre-oracles-criti...), and MIPS made a statement that a couple of their designs were possibly vulnerable (https://www.mips.com/blog/mips-response-on-speculative-execu... and this followup assumes that: https://www.mips.com/forums/topic/mips-mitigations-for-side-...)
The other vulnerabilities: Meltdown, Fallout, the recent MDS attacks (RIDL, ZombieLoad, Store to Leak forwarding), are Intel specific because they’re caused by the way Intel specifically chose to skip/defer security enforcement checks in parts of their implementation.
Other companies didn’t do this.
ARM, and IBM POWER and mainframe/Z also did that (Meltdown): https://en.wikipedia.org/wiki/Meltdown_(security_vulnerabili... ARM also has a Rogue System Register Read vulnerable design (https://developer.arm.com/support/arm-security-updates/specu...).