Looks like XeTeX really has no functioning support for the 2005 v.2 Indic script tags.
(This was discovered in bug 3511113)
I've particularly investigated the Devanagari ones.
Also, in dev2, 'dist' is applied after 'abvm' and 'blwm'.
Questions had arisen regarding a font that had specifications set to be activated
for either 'dev2' or 'deva'. I removed all the specifications of 'deva', and ran a test (attached)
which specified runs of script 'deva' and 'dev2'. Result: no lookups were activated for either