Hmm possible I suppose.
But I personally think that the Testatika uses, among other principles,
natural radioactive minerals in some of the "cans", a bit like Moray
used radioactive rocks in his "tube"s.
I also think the "wimshurst" part of it is not a simple "wimshurst" but
rather a combination of electrophorus and wimshurst, which could
well produce significantly higher static charge output. (polarised lucite
acts as the electrophorus' charge supply, motion produces movement
of these charges, which can easily be conducted through wires... and
the Testatika does use lucite/perspex "wimshurst" plates)
A form of electron valve is used to rectify the alternating output,
and I suspect the principle presented here
http://www.rexresearch.com/yablotch/yablotch.htmalso plays a role in the Testatika.
The above principles could, if properly implemented and coupled, produce
quite a bit of output.
And then there's still more elements that I do not have such a clear
picture of, but that undoubtedly lso play their roles in the device.
The Lindemann experiment using a magnet and a stack of copper and
aluminium plates seperated by a dielectric, that feeds pulses to a coil
around the magnet and receives an alleged output of hV DC directly
from the stack of plates, that is a good example of an element I
don't really get (yet). It is used in every Testatika but nobody really
seems to know what it really does or how.
Anyways, sure, I suppose a magnetic coating is possible.
But in my mind, the "cans" are basically electrostatic collectors
which are perforated to produce a larger surface area for interaction
with the ionised air in and around them.
I suppose the Testatika will remain a mysterious device untill someone
manages to replicate it independantly, or untill Methernita reveals
the secret. And I would not hold my breath waiting for the latter.

Regards,
Koen