I understand your issues and by no means meant to imply that this would be an easy item to resolve. I just noticed that this particular post was over 2 years old, and I've actually seen other similar posts dating all the way back to 2007 (see http://www.telerik.com/community/forums/reporting/telerik-reporting/summary-at-bottom-of-last-page.aspx
). It just doesn't seem like much of a priority to Telerik.
Regarding your specific questions though, I think at a minimum if any kind of footer is hidden/invisible, the space should never be "reserved" and unusable by other sections. If the developer wants to make this space unusable, I suspect there would be workarounds to that (adding panels with nothing in them, etc.). In the above link a Telerik employee provides a workaround. That workaround would not work for me (I know the product is newer now and has Conditional Formatting, but the end result is the same) because the footer that I want placed at the bottom of the last page takes up more than 1/3 of the entire page. If I put it in the Page Footer and hid it for all pages except the last, more than 1/3 of all of my other pages would be blank, and this is unacceptable.
Regarding whether or not to repeat group footers on all pages or not, I suppose this could be a property setting of the footer. You'd probably have to add another property setting to determine if aggregate values are over the entire group up to that point, or just aggregate values for the current page.
In any event, I do understand there is a lot to think about. My frustration is not that I think this is "easy", but that Telerik has had the opportunity to think about these things for many years now and hasn't come up with anything (specifically regarding the footer issues of course).
Also, there is no reason why these types of enhancements can't be rolled out in phases. There is no need to think through every single possible scenario before rolling something out. Many people have requested that they would like to be able to put a report footer at the bottom of the last page instead of immediately after the last detail/group. At a minimum I think that Telerik should find a way to make this available as soon as possible. It would still go above the last Page Footer, unless the Page Footer was hidden. If the Page Footer is hidden, that space should not be reserved and the Report Footer should go as far to the bottom as the margins will allow. Again, if the user wants to reserve the space where a page footer would otherwise be, they can simply add some extra space to the bottom of the report footer to make up for it.
Programmatically it may be as simple as taking the contents of the Report Footer and appending them to the Page Footer. If an existing Page Footer is supposed to be visible, just add the contents of the Report Footer before the contents of the existing Page Footer. If the Page Footer is hidden, remove the contents of the Page Footer, add the contents of the Report Footer, and make the Page Footer visible. This is just an idea off the top of my head, but it may be feasible.
I think that overall the Telerik products are great. I just feel like the Reporting is lacking some much-needed attention.