This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
[Moved to DR at the October, 2012 meeting.]
There is no limit placed on the number of c-chars in a multicharacter literal or a wide-character literal containing multiple c-chars, either in 5.13.3 [lex.ccon] paragraphs 1-2 or in Annex Clause Annex B [implimits]. Presumably this means that an implementation must accept arbitrarily long literals.
An alternative approach might be to state that these literals are conditionally supported with implementation-defined semantics, allowing an implementation to impose a documented limit that makes sense for the particular architecture.
Proposed resolution (February, 2012):
This issue is resolved by the resolution of issue 912.