The following PR replaces the sequence of statement

    d = d1.copy()
    d.update(d2)

(where d1 and d2 are dicts) with a form proposed in PEP 448:

    d = {**d1, **d2}

or equivalent.

Besides functools, where using the new syntax makes the code clearer, there are not much occurrences of such idiom: only in yet 5 files, 1-2 times per file.

3 years ago, Trey Hunter found 11 ways to merge to a new dict.
https://treyhunner.com/2016/02/how-to-merge-dictionaries-in-python/
He followed up with a performance comparison.
https://gist.github.com/treyhunner/f35292e676efa0be1728
** unpacking was nearly twice as fast as the 2nd place methods.
(Bigger dict might change the ratio, but I expect ** unpacking to remain first.)

Trey's summary: "This is simple and Pythonic. There are quite a few symbols, but it’s fairly clear that the output is a dictionary at least."  I consider the last point a major plus.

User comment: "Beautiful. Pythonic. Thank you."  No negatives.

New changeset da0847048aa7f934573fa449cea8643def056aa5 by Serhiy Storchaka in branch 'master':
bpo-36431: Use PEP 448 dict unpacking for merging two dicts. (GH-12553)
https://github.com/python/cpython/commit/da0847048aa7f934573fa449cea8643def056aa5

I hope the low number of such changes has clearly shown that we do not need the plus operator as yet one way of merging two dicts.