Known dose, sure. A lot of medical shops are posting independent lab measurements of all of the independent cannabinoids (most importantly: thc, cbd, cbn, cbg). So if you had a mg-accurate scale, and a bit of math, and assuming 100% uptake in a vaporizer, that's nearly a solved problem. With vaporizing the dried flowers, there is literally nothing else in there -- it's not an extract or anything where there could be latent glycols or butane or whatever.

So really, the problem _is_ solved :) It's just that the threshold and effective doses for cannabis mean that mg-specific dosing really isn't that useful.