Seems clear that both the adoption and "Hillary ties to Russia" explanations for the meeting are largely bullshyt. The former being the public explanation in case people asked, and the latter being the private explanation. Maybe both issues were discussed briefly but I think the meeting quickly moved to the point: we have these emails and will begin releasing them, in exchange you need to promise to lift sanctions. And as a sign of good will, change the GOP RNC platform in relation to Ukraine. Boom.
A big question: why was that chick still in the US? What if she was allowed to stay because she was secretly being monitored? What if the FISA warrant also included this meeting, meaning Trump Tower was under surveillance at the time...
If the Feds have that meeting on tape it's over. They'd likely wait for Jr to lie under oath, and maybe even wait to get Sr under oath too before revealing it.