I recall at least the (now discontinued) Qualcomm Centriq (Falkor) did away with 32-bit ARM (ARMv7, thumb*, etc.) and only supported the 64-bit ARMv8. If the market you're targeting doesn't value backwards compatibility, why bother?
Wouldn't surprise me if there are other A64-only chips as well.
Indeed. Both falkor and thunderX2 are A64-only. The backwards compatible A32 mode is optional only and not implemented by the ARM server vendors except Ampere eMag.
iOS 11 removed support for 32bit applications. Because the iPhone X requires iOS 11 I’m not aware of any way to run 32bit code on A11 processors and above. A32 support is likely already gone at the hardware level.
Wouldn't surprise me if there are other A64-only chips as well.