Will they update MM1 to MM3/Essentials monster damage? Doubtful.
Will they update the original adventure tools with Essentials monsters? Almost certainly not.
Will Essentials monsters (as well as MM1-MM3 monsters, etc.) be in the forthcoming online adventure tools? Probably.
Frankly, as much as I would love to see official updates to the MM1 monsters in the new adventure tools, I also think that their time is better used elsewhere, especially since I think it is fairly easy to adjust the current monsters if I want to. About the only official updates you might see (and no guarantee here) is where an Essentials monster stat block contradicts an MM1 (or other previous release) monster stat block. In those cases I could see them putting in just the Essentials version. (i.e. an Essentials wraith could replace the MM1 wraith and thus no MM1 wraith in the online tool).