SSE2 is supported by all x64 processors (SSE and SSE2 are literally part of the AMD64/x86-64 spec), so in terms of support, I don't see how that could be "relatively esoteric"...
And as a consequence if your compiler does autovectorization it will use SSE or SSE2, unless you specificly add compiler flags that make your binary incompatible with older processors (or you have an unusually smart compiler that adds seperate code paths for different CPU architectures)