2. Takes too much time.
No Solution! When the final portfolios come in, it's like taking two or three sets of papers home at once. So portfolios definitely will not save time. But I spend much less time on intervention drafts than I used to on final papers, and if I've seen most of the final portfolio pieces in draft, I don't have to spend as much time on them as I would on a brand new piece.
3. If students don't take the initiative to ask for intervention, some students can go for a long time without feedback.
Solution: Regular workshops will give all students frequent opportunities for peer review. Another Solution: occasionally, I require and pick up an intervention draft from everyone.
4. I spend so much time on intervention drafts that I have doubled my total grading time.
Solution: Comment on only the most significant feature of a draft (the element that will result in the most significant revisions).
5. Students do only superficial revisions.
Solution: Suggest students do as much writing as possible on a computer so that revisions don't require a lot of re-typing. Since I've switched to a computer classroom, I haven't had this problem. You could also require revisions of genre, audience, purpose, etc., to encourage students to make global revisions.