Would it, though? Unless you have evidence to the contrary, Phase 1 was not constructed to handle more than a single pair of tracks, Phase 3 is up in the air, and no maintenance facilities are planned for the alignment, which means any Phase 3/4 trains will need to come from either Coney Island (via the /, a long and arduous journey either way) or Jamaica (good luck without a complementary route!). The sheer lack of any indication that Bronx service is actually in the cards is itself rather damning.
For what it's worth, if a connection to 8th Avenue ended up being built and saw regular revenue service, I wouldn't bother sending the resulting route to the Bronx.