That is such an obvious and good idea - although it's dependent on enough people owning the game, which I don't think there were.
Even then the chance to make something like Left Behind as a standalone would have been interesting to see.
The amount of effort being put into the technology, while simultaneously creating the game, resulting in a fairly dry experience isn't surprising. But it would have been nice to see what they could produce as a downloadable experience knowing they their technology was already sorted.
Even a Resident Evil Mercenaries-like DLC, where they could focus more exclusively on showcasing the gameplay mechanics and retooling single-player areas for that mode might have helped.