If a computation can be a universe, and a universe a computation, then you're 90% of the way to Tegmark IV anyway.
The Tegmark IV hypothesis is a conjunction of "the universe is a computation" and "every computation exists as a universe with some weighting function". The latter part is much more surprising, so accepting the first part does not get you 90% of the way to proving the conjunction.
The Tegmark IV hypothesis is a conjunction of "the universe is a computation" and "every computation exists as a universe with some weighting function".
I interpret it more as an (attempted) dissolution of "existing as a universe" to "being a computation". That is, it should be possible to fully describe the claims made by Tegmark IV without using the words "exist", "real", etc., and it should furthermore be possible to take the question "Why does this particular computation I'm in exist as...
You all know the rules: