I think 700 x 700 is a huge image - some people don't even have screens that large (800 x 600) - 9 screenshots is also a large number - the vast majority of mods don't even have one screenshot.
You are talking about extreme and very rare cases, the current limits seem more than adequate for 99% of releases. It doesn't really seem to make much sense to set huge limits just for the odd rare occasion.