The Intel manuals list the set of features that are removed or planned to be removed from newer hardware versions: Sub-page write permissions for EPT, xAPIC mode, Key Locker, Uncore PMI. IA32_DEBUGCTL MSR, bit 13 (MSR address 1D9H), Intel® Memory Protection Extensions (Intel® MPX), MSR_TEST_CTRL, bit 31 (MSR address 33H), Hardware Lock Elision (HLE), VP2INTERSECT. AMD's manuals suggests that they view the ISA as purely additive, but I haven't read them in detail.

Basically, outside of MPX, and the confusing lineage of AVX-512 on client versus server parts, x86 is pretty strictly additive.