I had always assumed that a script that developed from the Brahmi
script was an Indic script - thus I would count Phags-pa, Lao (even as
in the modern writing system, and thus not an abugida), Balinese,
Buginese and Tamil as Indic scripts.
Peter Daniels has indicated that there are limits of time or place on
where and when an Indic script may develop - 'It turns out that you
have been talking about things that have nothing to do with the Indic
scripts, but with developments that happened many centuries later and
thousands of km away.'.
So, what do people consider to be an Indic script? I appreciate that
the boundaries may be fuzzy.