I think the primary disadvantage of an addition like this is the extra complexity is shifted almost completely into parsing. This means that accidental suffixes

I think the primary disadvantage of an addition like this is the extra complexity is shifted almost completely into parsing. This means that accidental suffixes on the end of literals always have to be treated as custom literals by the parser, until they can be confirmed as invalid by a much later stage in the compiler. In essence, an enormous class of syntactically invalid code is now syntactically valid and now just semantically invalid. A much harder bug to classify.