The planned tax reform by the Republican-controlled Congress could result in some uncertainty over the estate tax, according to the Wills, Trusts & Estates Prof Blog in "Trump Administration Sets Sights on Tax Reform."
It was previously expected that part of the tax reform effort would include a repeal of the estate tax. However, it is now uncertain whether that will remain on the table. It was also expected that repealing Obamacare would give Congress approximately a trillion dollars in total savings with which they could partially fund tax cuts. The repeal has not yet occurred.
With those savings not available, either some tax cuts need to be scrapped, revenue needs to be raised elsewhere or the federal deficit needs to be allowed to greatly increase.
If Republicans cannot agree on which of those things to do, they will need to compromise with Democrats to get anything passed and dropping the estate tax repeal is a potential olive branch.
Even though the focus has shifted to tax reform, nothing might actually be done for a long time.
The last major overhaul of the tax system was the Tax Reform Act of 1986. That legislation only passed after a long multiyear process, despite bipartisan support for the reforms.
Reference: Wills, Trusts & Estates Prof Blog (April 3, 2017) "Trump Administration Sets Sights on Tax Reform."