I think you’re kind of blazing a new trail here. Even the makers of Huel don’t normally consume Huel 100% of the time. They were originally going to pay someone to live on 100% Huel for a year, but that fell through. Instead, they got two people to do it for a month:
It could be argued that by being on 100% Huel you’re making things too easy on your digestive system because it’s already been broken down into a liquid. However, some nutrition experts advise we should actually be chewing solid food until it’s liquid before swallowing anyway.
But there remains the question of whether your body would eventually stop being able to respond to chewing in the same way it normally does. Another possible concern is that by having a limited range of food ingredients, your body might stop being able to produce digestive enzymes for some other foods; although could probably be remedied at a later date if necessary by taking a digestive enzyme supplement. But if you do seriously plan to only have Huel, never eating any other food ever again, maybe it would never actually be a problem for you.
Personally, if it was me, I would probably want to build up to it. For example, I would try a week on 100% Huel, then eat other food, then a month, then 3 months, then 6 months, then a year, then indefinitely. By going indefinitely right off the bat, you might be venturing into uncharted territory.