Modest proposal for a VTOL demonstrator
Take one Delta 4 LH2 tank and stick it in the middle of a Shuttle ET O2 tank. Instead of an RS-68 use an SSME surrounded by 4 RL 10's as in the delta graham. With careful engineering it should be light enough to land on the 4 smaller engines alone, but yet hold enough fuel for a 5 minute burn on the way up. Possibly could be used as a small booster (likely requiring delta 3 solids).