You could both open and close the DV window on a 707 - same mechanism and shape as the 737. I've done it so I know, and that was at 250kts. But I'm not so sure about being able to wipe the windscreen clean!!
I expect that it's a design hold over from the old requirement of CAR 4b: (my bold)
(b) Precipitation conditions. (1) Means shall be
provided for maintaining a sufficient portion of the
windshield clear so that both pilots are afforded a
sufficiently extensive view along the flight path in all
normal flight attitudes of the airplane. Such means shall be
designed to function under the following conditions
without continuous attention on the part of the crew:
(i) In heavy rain at speeds up to 1.6 Vs1, flaps
retracted,
(ii) In the most severe icing conditions for which
approval of the airplane is desired.
(2) In addition to the means prescribed in
subparagraph (1) of this paragraph at least the first pilot
shall be provided with a window which, when the cabin is
not pressurized, is openable under the conditions
prescribed in subparagraph (1) of this paragraph, and
which provides the view specified in that subparagraph.
The design shall be such that when the window is opened
sufficient protection from the elements will be provided
against the impairment of the pilot's vision.
I have no experience doing it an an airliner. However, I did hit a swarm of some kind of black bugs while flying my flying boat. I was low down, so it's not so surprising. My only option was to open the side window, and wipe off enough to see to land in the lake I was crossing, and wash them off. Later I went to the beach, and washed off the leading edges of the wings and tail, which were also black!
I had the windshield of a Cessna 310 iced over a long time ago, with no alcohol in the tank. I was able to reach out the parking ticket window, and pry off enough ice to see to land.