SPARC, MIPS and PowerPC may be fringe but they are still out there in the fringe for servers and/or supercomputers.
Several CPUs of each architecture were released in 2017.
IBM's POWER chips have supported the full PowerPC ISA for a decade and its performance is very competitive to Intel XEON, if not surpassing.
Oracle (which had bought Sun) closed their SPARC processor group last year though. Fujitsu may still be active.
Chinese Loongson makes MIPS processors at 1.5GHz, but they would need to step it up to compete.
I have not checked PowerPC or SPARC but MIPS is not vulnerable to Meltdown. Linux on MIPS can not leak any kernel pages -- simply because MIPS does not do paging in kernel mode.