I once tried doing something like this in ACT (as a plugin) but due to the volatile nature of haste with bards around, it was usually off. There's another
thread in Requests that talks about doing the calculations in the UI. It doesn't sound like either solution can do it alone very well.
I suppose a simple UI that exports(to chat) the haste values at the end of a cast would work better if be messy. The final problem being dual wielding characters. For a DynamicData based mod, I suppose SoE could be nice enough to add both weapons as separate data. But a parser based solution could not tell the difference between two piercing weapons for instance.