I also share Brightblades excitement if this turns out to have any validity. :)
As to your actual question, there is very little written about this idea that doesn't seem to be an exact (or nearly so) duplicate of the phsyorg.com article. Space.com, New Scientist, and Universe Today being the more popular.
All seem to agree on (from the New Scientist) some of the calculations used, however the validity must await the arrival of the probe.
Density measurements suggest a rocky core fills 40 per cent of the dwarf planet's volume. If the core contains potassium at a concentration of 75 parts per billion, its decay could produce enough heat to melt some of the overlying ice, which is made of a mixture of nitrogen and water.
He points out that Earth, which probably formed with less of the volatile element due to its closer distance to the sun, has 10 times that concentration in its core.
This paper (PDF) does run some of the math for you, but again concludes with that we need to observe the body before making a final determination.
This paper (PDF) goes into A LOT more detail. They conclude with:
Our results may be summarized as follows. Whether or not Pluto
develops an ocean depends on the rate of heat transfer across
the ice shell compared with the heat produced by radiogenic
elements (McKinnon, 2006). We find that, for the nominal
potassium abundance, there is a critical reference viscosity above
which an ocean develops. For reference viscosities in the range
10^13 - 10^15 Pa s vigorous convection occurs and an ocean never
forms. For reference viscosities >4.16 x 10^15 Pa s, convection is
either sluggish or absent, and present-day Pluto possesses an ocean
of roughly 165 km thickness beneath a conductive ice shell 165 km
thick. If the core is sufficiently depleted in potassium, an ocean
never forms irrespective of the reference viscosity. Without an
ocean during Pluto’s past, surface tectonics will be predominantly
extensional (perhaps with minor recent compression) and a fossil
bulge may be present. For cases which possess an ocean, there is
no fossil bulge, and compressional surface stresses should dominate
(perhaps with minor recent extension).
This study does not include the presence of volatiles such as
ammonia, which are likely present and may have an effect on Pluto’s
thermal evolution. The main effect of incorporating ammonia
is to produce colder ocean temperatures and thus generate ice
shells which are more likely to be conductive. Ammonia thus increases
the likelihood that Pluto currently possesses a subsurface
Yep, freakin' awesome! But keep in mind - we really don't know what the little guy is made of, so all this is still quite a bit of conjecture. 2015 will be the telling time when Horizons gets there.