Well, I finally got around to doing some testing on 100.0, and GPKs from 10.3.1, 10.4.1, or 10.5.0 all bomb when started up. I can start up an MPK fine, but it doesn't display rasters; however, I can display rasters separately, so that's not a big issue. Also, TPKs and tile caches with custom tiling schemes won't display. CORRECTION: Runtime doesn't like custom tiling schemes with only one scale level defined. If I have two or more scale levels defined, then the TPK is displayed between the minimum and maximum scales.