I've been working on a workout editor over the Christmas break. Its not done, but lets you edit ERG files and get the MMP and W'bal plotted as you go.
I've just re-used the sustained interval algorithm to find aerobic efforts that are impossible (at least according to the model anyway). It highlighs sections that are impossible with a red line along the x-axis.
Because it is so fast we can search every time the user drags a point. Really pleased with the results and TBH feels like the best use of the algorithm !