Would there be any reason for us not getting developer beta 4 this week? Only reason would have to be because of too much downtime during the week of 4th of July making development halt for a short period making us having to wait three weeks instead of two weeks between beta 3 and beta 4.
Normally we should be getting new beta's every two weeks at this point in the cycle.
Recall that these betas have existed for some time before we see them. Apple, internally, is testing these several weeks before we see them. So, other than the possibility of some disruption due to the bad “f” build of the current beta, the next beta version is teed up and ready.
The question is: today, tomorrow or later this week (to allow as much time to pass and data to be collected on the revised “g” build as possible). Given the continued preeminence of the iPhone 7 (#1 globally, see chart below) and the iPhone 7Plus (#6), and the fact that these were the phones affected by the bad build, I’d say there’s a decent chance Apple will want a few extra days of data before releasing the next beta. On the other hand, they have now had a week, so that may be enough. On the third hand, they are on a tight deadline and they can’t wait too long to release to be able to release in time to hit the September deadline.
My guess, then is 12.4 today and 13.0 beta 4 tomorrow. They might have done it the other way but for the build failure.
Finally, the the July 4th holiday: this is a known impediment so they definitely plan around it. It has not impacted other years (see 2nd chart below). iOS 11 had its own issues with beta 2 so should not be considered.