The new clue the abstract is referring to are the nodules and deposits recently found near Home Plate by Spirit with the extraordinarily high silica content. The authors are suggesting this material might be the origin of the Type 2 material:

"Recent Mini-TES observations in Gusev crater
(beginning on sol 1101) have for the first time revealed
material with a feature remarkably similar to the 465
cm-1 feature found in ST2 material (Figure 5). Three
separate occurrences separated by many 10s of meters
of very rough textured, highly eroded outcrops with a
nodular appearance have the same Mini-TES spectral
character. Although the 465 cm-1 feature strongly resembles
that of amorphous silica, the middle wavenumber
region (~800-1200 cm-1) does not. The surfaces
of these outcrops are heavily contaminated with
soil that perhaps distorts this part of the spectrum.
Additional observations are planned to address this
issue."
...
"High silica amorphous phases thus remain
as the best candidate components of ST2 material,
although we cannot distinguish between primary
and secondary forms using our methodology."
NEW CLUES TO THE ORIGIN OF TES SURFACE TYPE 2 MATERIAL, p. 2.

That is why I was mentioning the discovery of the amorphous silica by Spirit near Home Plate in my post. Note the MER rover scientists suggest this amount of amorphous silica content is usually associated with aqueous processes.
I was proposing aqueously altered rhyolite to explain the high silica material in Gusev. This material does not necessarily have to retain a high hydration content though it is formed from chemical alteration by liquid water.
If these amorphous silica nodules and deposits in Gusev are the origin of Type 2 material and if altered rhyolite is the origin of the amorphous silica in Gusev then the altered rhyolite would be the origin of the Type 2 material.
However, I should say a problem with this interpretation is that the Type 2 terrain on Mars is typically dark colored, while the amorphous silica nodules and deposits in Gusev are light colored.

Bob Clark