Something that could help new users, and would have zero impact on run-time performance is to add a warning a parse-level for the literal 10 to literal integer powers that overflow. The warning would read something like:
“The expression 10^21 results in integer overflow. To avoid overflow, use 1e21 for a floating-point value, or big(10)^21 for a BigInt. Write (10)^21 to compute an Int64 without this warning.”