Tax cuts are almost never retroactive.  That is very difficult for the IRS, and it may be unconstitutional to raise someone's tax retroactively.  (It's not unconstitutional to lower someone's tax, but any new tax plan will probably have winners and losers.)

You can wait if you want, but the most likely situation is that taxes will change for 2017 and going forward but not going backward to 2016.  If there are backwards changes, you would be able to file an amended return.