You really only suggest this? And call that 3.0? I think you misunderstand the purpose of this document.
Anyway, reducing memory usage is done in every GNOME release. It wasn't included in the final release notes, but as just one example, pango uses 8MB less memory with certain fonts. There are various other examples.
Further, seems you missed out on the part where we'd remove usage of the deprecated libraries. When those are all removed, memory usage will automatically drop (as those libraries won't be loaded anymore).