Nestle produces something called Modulen specifically for people with IBD. The idea is for people with Crohn's to switch to a liquid diet during bad flare ups to settle things down as digesting food causes inflammation.
It is rather expensive. Luckily for me, my insurance covered it (I'm from Israel, so YMMV). The hard part is that you have to pound a dozen glasses of the stuff every day. Some people can't even drink that much water and this is a heavy drink.
Soylent may be an improvement in terms of price and preparation because Modulen comes in powder form and doesn't mix well with water and goops up quickly. It is simply not easy getting it down.
To those of you suggesting this sort of thing can solve world hunger - doubtful. I'm the only one my doctors know of who actually was able to adhere to a liquid only diet for a stretch of multiple months, people simply don't have the willpower.
You miss food quite badly and are never satiated. What I think Soylent could possibly be is an ultimate supplement, like a protein shake - in fact, fitness companies like Beachbody (P90X) hawk all kinds of dubios concoctions, it is a lucrative market. One that actually works would be neat.