The Solicitor General was invited on Jan 07, 2019 to file a brief in HP V B case expressing the views of the United States. Looking at the data set from 2001 onwards reveals that the solicitor general takes, on an average, over four months to file the brief.

That brings it to April/May 2019 time frame.

I think the timing of SFOR filing is very close to HP Vs B Solicitor brief and congress going for Stronger Patent Act eliminating Alice and section 109 supporting small business patent owners.

Could have Solicitor surprise any day.