The reworked description of the Spellcaster's Onslaught ability says the additional 1d10 di from a critical hit are added to to the weapon hit damage roll:
This weapon deals an additional 1d10 elemental damage on a sccessful crit..
(note, there is a small spelling error in the description)
Example with an x2 crit weapon:

However, it appears this additional 1d10 is also being added to the critical damage roll for a touch spell delivered via spellstrike through the same weapon hit. This would appear to be double dipping on the added 1d10 crit damage since it is not a separate attack by the weapon.
Example from same hit above:
