Australia tried Bancroft with Warner to open....Marcus Harris and Warner and both didn't went quite well. I think Finch with Warner as opener would be good. They both have a good chemistry while opening in ODI's and I think wouldn't be a problem if the format is changed.
They tried several combinations, and all of them failed. Warner, Harris, Khawaja, Bancroft.etc were unable to perform on a consistent basis. IMO, they should drop all these four players and give chance to some young player. I don't remember the last time a teenager made international debut for Australia. Even Ricky Ponting was 20-years old when he made his test debut back in 1995. Their first class cricket is also aging, and the senior sides usually don't field any teenagers (on the other hand in India and England, you can find so many teenagers representing the domestic sides).
Warner is 32 years old and Khawaja is also of the same age. I don't see a point in offering them a slot in the playing XI, at the cost of some younger player. Warner is essentially a T20/ODI player and including him in the test side can be justified only when there is no other option. Usman Khawaja has failed consistently during the last few years and his bating average is not what you may expect from someone who has played 44 tests for Australia. There are talented players available in Australia such as Matt Renshaw, Will Pucovski and Ben McDermott and the selectors should give them a chance.