Looking at the settings in the current build, I see that "messages to keep" goes to 10,000. It's that way for a while now, actually.
This is a Galaxy Nexus, on smaller screen devices I suppose some scrolling might be necessary to access the items at the end of the list....
As for offline mode, yes, that's something I'd like to do. I often see those things in the sky, called planes, and there are people inside... and bad cellular coverage areas, too.