Let me stress that you can drag the tabbles in such a way as to replicate the arrangement you had with categories (and with more freedom.) This is not going to take forever, and you only have to do it once.
You may object that tabbles are not aligned. Two answers:
1) I am planning to implement "snap to grid" . (if approved by my colleagues.)
2) However I am afraid it will not work well when we make tabbles scale automatically according to their files. (see the blog post about this)
I mean, all tabbles will have different sizes, so even after auto-aligning and snapping to the grid, it will not look good. What do you think?