Even in the case of the Milky Way blocking the light, we could probably do the math to estimate would an observer would see if they were outside the Milky Way, interpolating from the observed IR/UV and some model of the visible spectra would be be without the local interference. Or is that infeasible in some way?
Certainly some phenomena just don't have much visible light of interest - so shifting the the spectra is inherently necessary in those cases and is thus inherently subjective.
Not necessarily, various objects can look completely different in different wavelengths and it's not really possible to interpolate without taking a picture of each part of the spectrum.
The Milky Way and the entire local group of galaxies are flowing towards the superclusters located directly on the opposite side of the galaxy, and there's huge (thousands of light years) clouds of gas and "dust" (supernova molecular feces) that are like actual, thick, opaque storm clouds that form a donut around the galaxy, so it's impossible to "see" where we're headed except for the the X-rays and mid-infrared that doesn't interact with the huge clouds. And we won't be able to until we can leave the plane of the Milky Way's disk, or we build a telescope that is 2 dozen orders of magnitude more sensitive than anything we have so far.
Certainly some phenomena just don't have much visible light of interest - so shifting the the spectra is inherently necessary in those cases and is thus inherently subjective.