Was thinking about that today. I have two theories:
1) the John Koskinen impeachment hearings currently taking place have monkeywrenched their plans. Any further hinky doings from the IRS are simply too risky at this point.
2) Trump’s tax records are actually clean and he knows the Dems really have nothing on him.
Hopefully #2...If his tax record is clean, I can see how they might be waiting to release them when the Democrats are at their biggest uproar about it, about 2-3 weeks before the election. A clean tax record will send them over the cliff, because they truly believe there is some fishy stuff in the returns.