As far as Boost.Phoenix, what are the concerns?
The problem is that both units and phoenix seem to requiere a fair amount of glue (template) code. Mainly it needs to translate the units::*_typeof_helper protocol to phoenix::result_of_* protocol, this is needed for quantities, references of quantities, units and other type with which quantites can interact with (e.g. double) the that I managed to add is long and very repetitive and probably still limited. Also I hesitant to invest a lot of effort since something seem to be different with the upcoming Phoenix3.
Certainly, if all that is involved is to provide result_of_* classes that forward to the *_typeof_helper classes that should not be a big problem. A small demonstration of the problem in integrating Boost.Units and Boost.Phoenix, along with a proposed solution, would be a great starting point. Matthias