It's my understanding, though I still can't find anything confirming it, is that the changes to the tax law being worked by the present administration, start for the 2018 tax season, and are not retroactive for the 2017 tax season.
It appears from reading the headlines that new mortgages (i.e., refinances) would be subject to the $750,000 cap. However, this is not definitive, and perhaps this is not correct, or refinances already in progress will maintain the $1,000,000 cap.
