Rationale (July, 2020):

This issue is essentially about implementation limits, which are impossible to specify normatively, and it is inappropriate to specify the desired and forbidden implementation techniques in the Standard.

Paper P0913R0 proposed adding support for a symmetric-transfer capability intended to allow coroutines to be recursively resumed without consuming an unbounded amount of stack space. However, the current wording does not required this, only suggesting it in a note in bullet 5.1.1 of 7.6.2.4 [expr.await]. This should be a normative requirement.