20.3 in N2798 is very stable, since except for the diff markup it is the same as the Committee Draft that is currently being reviewed by national bodies, and there are no outstanding issues in the LWG active issues list.
Why the ugly (and pointless) ratio_multiply? Shouldn't there just be a standard template for multiplication? This can then be specialized as needed for any types that can be multiplied at compile time, which facilitates code such as used in the Boost.Units library where the result type of multiplication of two units takes into account the possibility that the type of the product of two other types is different. As far as I can tell, all having a special set of arithmetic operators of ratios does is necessitate the use of another layer of indirection. Maybe I'm missing some clear benefit? I think what Cromwell is talking about is coming up with extensions to MPL to do compile-time mathematical operations, which would be neat. Steven came up with a basic compile-time linear solver for Boost.Units, but it would be extremely cool to have this functionality abstracted out into a more general library... Matthias