Touring on meal replacements (Soylent or alternatives). Anyone tried? Thoughts, impressions?
Just living off that stuff requires your digestive system to adjust, so if you try it you should build it into your diet well in advance, and as a major component. Don't forget to take into account how much extra you need compared to a typical lifestyle. 

It can't really save you any weight compared to other dehydrated foods, as a gram of carbs is a gram of carbs (same for protein or fat) , but it might save you some bulk compared to something like ramen (with whey powder drinks on the side). For all dehydrated (i.e. lightweight) options access to water is critical. 

A further thought is that if we accept that these are perfect/balanced/complete nutrition as they claim, then complete for what? Your energy needs when touring will go up (assuming you're ordinarily fairly sedentary), but not all your micronutrient needs will (to some extent your body can adjust these), and fibre could go either way.  Sodium needs will depend on how much you sweat, which in turn depends on you and the climate as well as the effort level.

On the other hand I was reading recently about a solo tour on remote roads fuelled by ramen. Even though he didn't really have enough, I got the impression he was sick of the stuff after a week. 

There are advantages to these products: they don't need cooking, saving time and fuel.  In the extreme case that could mean not carrying a stove or cooking pans (prepare it in your water bottle).  However in most climates I reckon most people would want the ability to have a hot meal or hot drink, and if you're relying on finding water, boiling it is a good idea (though I'm told that  unflavoured Huel is disgusting, maybe water treatment tablets would improve the flavour!).

Overall I can see a role for them as part of a diet plan, so long as you've got good access to water and get on with them.