Here's a thumbs-up for Qarl's suggestion. Couldn't it be implemented using wireframe rendering until the texture is loaded using a pulsing wire color that fades/de-saturates with distance?
So on first load on a slow connection, everything might look like red or blue wires and "reality" fills in from closest to farthest as textures are downloaded until the render limit is reached.
I also like Hamlet's suggestion of bundling LR content into the viewer, although frequent changes to the landscape could undermine that. Perhaps separate "common SL content" could be downloaded as modules that are saved with the client and updated as needed? These should be the most common LL-owned textures, sounds, scripts, and objects that are used in SL and available for others to use for their own builds to lower bandwidth demands.
Wonderful thread ... good going Hamlet!