But wouldn't the sensory input be completely missing? A fetus at least has some of these inputs as the sensory organs are developing, which is part of getting sentience. A brain in a vat has no equivalent so it would lack a lot of additional input that usually goes into forming a human consciousness/sentience.
Deaf-blind individuals still exhibit consciousness. There are people who can't smell, or feel touch, or temperature, or pain. How many senses do you have to remove before consciousness goes away?
If consciousness can exist with the absence of senses (e.g. if you were cut off from your senses for five minutes), then who's to say it can't develop without them? We don't know that consciousness requires sensory input; is it safe to assume that?
There's a lot of different inputs and outputs to organize and understand before the brain can even begin to make sense of the world outside the body. In that sense, yes, the brain needs sensory inputs to assert itself, but our traditional "five senses" are but a small subset of the sensory input the brain receives and must process.
Afaik it's somewhat established science that taking senses away leads to developmental differences in the brain.
And in this case we are not talking about one or two of them missing, we are talking about all of them missing.
So it begs the question if it's actually possible for consciousness, in the sense of sentience, to develop in a sensory vacuum?
I believe there is some phenomena related to the way people born blind visualize or think about things, but I only vaguely remember reading about such things.