Some interesting dialogue on other web sites about this. Specifically, who gave the emails to the NYT to force Donald Jr. to release them in advance. 
The obvious speculation is James Comey as he was seen entering the building a couple of weeks back. The NYT then sat on the story until after July 4th and the G20 for maximum theatrical impact. Business as usual so far.

The interesting theory is that this meeting was a total set up so that Omaba could have a valid reason to get a FISA warrant to actively monitor the Trump campaign. Recall that Trump has previously said that there was real evidence of this. (i.e. certain outside people had knowledge that could have only come from the campaign team.)

For those who do not know what a FISA warrant is, try this...
https://en.wikipedia.org/wiki/United_States_Foreign_Intelligence_Surveillance_Court