FileAPI use case: making an image downloading app

Sorry if this has been covered before.

I've been wanting to write an app to download images from photo sites and
I'm wondering if this use case has been considered for the FileAPI wrt
Directories and System.

If I understand the current spec it seems like their are some possible
issues.

#1) The spec says there is a 5000 file limit or directory.

#2) The spec requires an app to specify how much storage it needs

I understand the desire for the limits.  What about an app being able to
request unlimited storage and unlimited files? The UA can decide how to
present something to the user to grant permission if they want.

Arguments against leaving it as is:

The 5000 file limit seems arbitrary. Any app that hits that limit will
probably require serious re-engineering to work around it. It will not only
have to some how describe a mapping between files on a server that may not
have that limit, it also has the issue the user might have something
organized that way and will require the user to re-organize. I realize that
5000 is a large number. I'm sure the author of csh though 1700 entires in a
glob was a reasonable limit as well. We all know how well that turned out
:-(   It's easy to imagine a video editing app that edits
and composites still images. If there are a few layers and 1 image per layer
it could easily add up to more than 5000 files in a single folder.

The size limit also has issues. For many apps the size limit will be no
problem but for others....  Example: You make ray tracing program, it traces
each frame and saves the files to disc. When it runs out of room, what is
its options? (1) fail. (2) request a file system of a larger size. The
problem is (2) will require user input. Imagine you start your render before
you leave work expecting it to finish by the time you get in only to find
that 2 hours after you left the UA popped up a confirmation "this app
requests more space"

The same would be true for an image downloading app. You start the app to
download a 1000 images, not knowing their sizes before hand. You start it
and leave. Half way through the UA puts up a conformation asking for more
space.

Have these use cases already come up and been rejected?