Anthony Matonak wrote:

... I've heard reports that there were other issues with
the beadwall system. For instance, the foam beads would
break down over time.

Not exactly. They tended to clump if never cycled.
IIRC, cycling once a month would fix that.

"Replacement foam insulation" (filling the space between two glazings
with soap bubble foam at night) seems more practical.

... I question it's usefullness in a house. For instance, how clear and
streak free are the windows when the foam goes away?

Moreso than my $500 500 ft^2 cloudy plastic film sunspace :-)

How do you insure that the window cavities are sealed well enough that
they don't ever leak in some hard to detect fashion and cause damage to
the structure?

I'd probably make the "windows" with 2 layers of 0.020" clear polycarbonate
from a 48" roll, over plastic 2x4s, with lots of silicone caulk.

... how do you design the windows so that they can open?

You don't. A few plain windows might do that.

How about this for a possible solution. There are double pane windows
being sold now that have window shades or blinds inbetween the panes.
Mostly, this means that they never get dusty and you won't find the
cat has hung himself from them. Air is a pretty good insulator except
when there is some kind of circulation going on.

Even tiny circulations.

A cellular shade could be produced using thin mylar or paper such that
it folds up into a small space at the top or bottom of the window cavity
and yet can unfold to fill the entire space with small air-filled pockets.

It could be...

One or more layers of aluminum coatings could be added as well to
help cut down on radiant loss.

Good idea. Scheme 18.7 on page 168 of Bill Shurcliff's 1980 Brick House book
"Thermal Shutters and Shades" describes 5 sheets of metallized Mylar with
springy spacers that unfold when it's rolled down. Scheme 18.8 on page 170
describes an interesting self-inflating Mylar shade. Alas, these are no longer
being made. Perhaps they can be recreated with an iron or a $118 -RS1 hot
roller for plastic film seam-sealing from Hillas at (800) 952 7274.

Symphony "energy track" shades with tracks on each side to reduce air leaks
are fairly expensive and low performing. They (877) 966-3689 say their room
darkening shade has a R-value of 3.2, when used with an R1.8 window :-) This
increases to R4.8 with side tracks. A 3'x6' shade costs $170 with the tracks.

Tiny cold soap bubbles can have the same R-value as fiberglass. A 6" window
might transmit 80% of the sun during the day and become an R20 wall at night.

Nick