Subform is generally a great functionality, I do believe it is limited so far in Zoho.

1.       It displays all fields from the form. What if I only want to display some fields?

2.       Can it be sorted?

3.       It would be nice to have more of view like capabilities ( sum calculations), Ui

4.       If I have File Upload in subform, how do I see it? I think it should behave more like view in that case

5.       This is a different discussion, but I think File upload field, should allow some kind of option to get to the uploaded file also from the form, currently this functionality exists on the view only