Yep, that's my question.
I know the Essence was made with a body as small as possible, but I don't know if "as possible" allows for an upgrade path. Europa electronics? Rogue electronics? The full Series II kit?
I ask because I love my Essences. Ergonomically, I haven't found a more user-friendly instrument at any price.
My recollection is that the short answer is no. Looking through the examples on the Essence page at alembicguitars.net, there are some with Europa, Signature, Anniversary, and East-Meets-West. But my recollection is that these require larger control cavities carved when built; and my recollection is that some, probably the Anniversary in particular, were quite tight. My guess is that Series would at the very least require a thicker body, and it may be that the circuit board is just too big.
If you're thinking of a new build, then talk with Mica and find out what's possible and what's not.
http://alembicguitars.net/prod/essence.html (http://alembicguitars.net/prod/essence.html)
The short answer is no.
The medium answer is on a custom build you'd have to make the body thicker to accommodate the parts, and not everything will actually fit, you can do something like Will Gunn did here with "Refinement I and II. (http://www.alembicguitars.net/info/fc_refinement.html) He uses an SF-2 as the tone controls.
Otherwise, you'd have to modify the body shape to cram it all in there, and then, it won't be that Essence body shape you love.
Europa/Rogue do fit well (on a new build - hard to make them fit existing holes). We've crammed Signature electronics in there, but it is really really tight (hope you have skinny fingers!). Face-mounted jacks give you more room than side-mounted ones do.