Thanks again for your very informative and enjoyable preview!

here are the few things i noticed:

"(the first superscalar CPU in a Symbian phone)"
this is not a symbian phone

"memory available for installation of 3rd party software (i.e. actually the whole rootfs file system) seems to be limited to a relatively small capacity of about 256 MB "
i remember reading somewhere here in this forum that this actually won't be a problem, because the rootfs is supposed to be around 1 GB in the final version. i can't find the source for that any more, so i guess it still remains a rumour
what i did find was this thread. the mailing list linked in the last post is a good hint that many applications have already been modified to use /opt, so the small rootfs (if it stays small) shouldn't be that bad an issue as you make it out to be.

"enabling USB host mode"
information on that is somewhat limited, currently it's all speculation.
it might be only a software issue, maybe a small adapter is needed, but it could also be that it won't work at all. the only thing that is certain is that there's no official support.