I also agree with Qarl -- While gray is better than "TEXTURE LOADING" all over the place, it looks horrible. Just have the default texture be a black square with blue glowing border. Would be easy to do.
I have thought about having a couple of spots where local data is present and used. Sort of a permanent cache of stuff that's in that area. I concluded it was a bad idea. For one thing, this permanently sets the design of the sim in cement, rendering it forever unchangable. For another, you now have additional checks everytime a prim is rendered, having to check to see if the sim is the predefined one and all data coming from the additional cache. And making the viewers 250M will not bring new visitors to our virtual world. In fact, such monsterous file downloads would make people give up before they even tried it out.
And most importantly, it would create a false expectation about what they should experience in the rest of SL. If there will be lag and simcrossing issues everywhere else, hiding the problems in the newcomer area will only delay the results, not change them. Someone quitting because of the serious problems inworld is still going to quit when they get their first real taste of how the system functions. Better to give a customer realistic expectations early on than to make them angry that you tried to sucker them at the beginning.
