@Frederick Ding - Hey there, nice to see there is someone slated to spend a bunch of time on the importer and the other portability issues of WordPress. The issues addressed in this post and on the support forum are not recent, but have existed for quite awhile.

A few suggestions I had:

It doesn't matter what information is exporter whether it's everything or just posts, or pages. If the person chooses to download attachments, those should be moved over with the content. Currently, the only way to get attachments from one place to another is to select the option to export EVERYTHING.

Images should be properly attached to their corresponding posts

Image source URLs should be changed to reflect their new location.

I'd like to see some sort of progress or information bar that shows what is happening during the import process. It sure is a drag to just sit on a page and watch a spinning circle without knowing if the import broke or not.

If I think of anymore, I'll publish them in this comment thread.

Good luck Frederick, you have your hands full.