I don't think it will ever come out, because of the safety issue. Too much power equals too may law suits for GM. If you want a 7.0L in a truck, by a RCSB with a 4.3L and convert it to a 7.0L, but you will a 6.0L block as a starting point, GM sells them for about $700 (bare block only).

 

The price tag alone would cost sales, no matter the engine used at that power level. Plus they'll have to deal with a stronger transmission, etc. and that will drive up the price even more. If they build it, 50K would probably be a starting price and most people want a bigger truck or a pure sprots car for that price range. Besides, what would people do for performance enhancements if they start with 500hp? Seems to me that would remove the average enthusiast altogether. I won't be holding my breath to ever see such a beast from the production line.