It would be great if we have one more upper level in a catalogue - say, "Catalogue of Catalogues" and an opportunity not only import photos from another catalogue but simply ADD (or connect) another catalogue to existing one. The idea is, when your archive is relatively high (mine is about 15 TB) and you have one catalogue for all, LR goes slow. To avoid I make separate catalogues per session or per travel, per client, etc. But when I collect photos for some project, album or something like that I need to search through the whole archive. The proposed upper level could provide only Search and Make/Add to Collection features trough all included catalogues, and when you go to Develop a smaller catalogue is opened and you work as usual. Included catalogues in Library could look like folders with some special mark. Other modules of LR if entered from "upper" level should work only with collections made in this level. To my mind, it could be useful.