Good questions. The kind of examples this rule is meant for are the ones below:
(1) the other.masci 3fS-order daughter 3fS-throw-3mOi river
"The others she ordered her daughter to throw (them) into the river."
(2) 1S-want 1S-tell 3mSi-believe=REL and 3mSi-make=REL matsigenkai.
“I want to tell what they believe and what they make, the Matsigenka.”
(3) 1POSS-brother.in.lawi 1S-leave=3mOi 3mOi-pursue monkey.
“My brother in law I left pursuing a monkey.”
(4) Kinteronii PRO.MASCi be.master.of earthquakes
"Kinteroni is the master of earthquakes"
(5) that PRO.first.onei 3mSj-make=REL Godj personi [3mS-name-3mO NAME and NAME].
“Those first people that God made […he named Kinteroni and Pareni]”
There’s both a left-dislocated (1, 3, 4) and right-dislocated (2) position, and it can coreference with either a standalone pronoun or an affix, but critically it must be one or the other.
Certain free pronouns must be coreferenced with either an agreement marker (not shown) or an NP in a filled gap (4). We discussed not giving these pronouns a pron_rel.
The reason I wanted initially to allow NPs to resumpt was (5), where it would be [O-GAP] [VSO], but I think I can bracket that one so that it is [OVS] [O-GAP]. This keeps the pronoun VP-internal, so the pronoun can introduce the gap.
I don’t see the extr-subj rule in the Matrix version I have. Assuming it’s something to generate from the customization system, but I’m a bit out of time today to go generate it, and will look into it Friday or next week.