Many thanks, Oren and Ilan. That gives us a lot more breathing space.
Regarding the number of prims, we're already limiting that to practical numbers based on several factors, so that's not an issue. The reason the RezMela engine stores relatively large volumes of data is that each object in a scene can potentially have a lot of associated metadata, as well as such things as the text displayed on a sign, potentially long URLs for web addresses, etc. This data is stored centrally (partly so that it can be serialised to notecard at the time the user saves the scene), but needs to be rapidly accessible - and changeable - during operation.