This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
The description of the numeric literals occurring as part of user-defined-integer-literals and user-defined-floating-literals in 5.13.9 [lex.ext] says nothing about whether they are required to satisfy the same constraints as literals that are not part of a user-defined-literal. In particular, because it is the spelling, not the value, of the literal that is used for raw literal operators and literal operator templates, there is no particular reason that they should be restricted to the maximum values and precisions that apply to ordinary literals (and one could imagine that this would be a good notation for allowing literals of extended-precision types).
Is this relaxation of limits intended to be required, or is it a quality-of-implementation issue? Should something be said, either normatively or non-normatively, about this question?