Here are some of my ideas. They are changing frequently.

Fill free to add yours.

===== Paging class =====
Probably with some kind of data_source classes to which will have same interface so that they could be easily rendered. For now I think that this should be implemented as separate lib.

===== Attributes =====
Solution for adding display attributes. I think that best will be in form:
<code php>
$attribute->required->style = "color: red;";
$attribute->normal->style = "color: blue;";
$attribute->error->class = "error";
</code>
This solution is implemented in kodform4.

===== XForms =====
Should have support for xforms but as separate classes or member function ( $form->displayX() ).