This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
A ud-suffix is defined in 5.13.9 [lex.ext] as an identifier. This prevents plausible user-defined literals for currency symbols, which are not categorized as identifier characters.
Rationale (June, 2014):
CWG felt that a decision on whether to allow this capability or not should be considered by EWG.
This is a request for a new feature, which should be proposed in a paper to EWG. SG16 recommended not adding the feature.