Why the hell want you to use litterals beginning with numbers ? for years, most programming language have forbiden symbols beginning with numbers, i can't see the benefits of such a feature. To me, it is nothing but a bad idea...
About the support of hexadecimal notation, i had though about adding such features for my own project. But i realised that the support of hexadecimal values (refering to "integer hexadecimal") wasn't interesting since hexadecimal notation is only interesting if logical and bitwise operation are available, and that does not make sense as libmatheval is designed for floating point features...