In that conception, the bullet would kill the person, but the soul would still exist to find out about it, allowing for collapse, and ultimately escaping the ridiculous solipsistic notion that your body is necessary for reality to exist.

Biocentricism, in my opinion, works best with atheism. If there is just a wavefunction evolving endlessly and unintelligently, the second it produces consciousness, the entire past collapses from there. Biocentricism then is not remotely idealism, but as it were, solipsistic materialism, of the same sort as the proponents of the weak anthropogenic principle, only much worse.

There are other problems with the idea presented here, though. Even if an intelligent observer is necessary to resolve reality out of a condition of vague potentiality, so what? Why should it be necessary for reality NOT to be in a condition of vague potentiality?

Secondly, quantum mechanics is not self-evidently true. It must be justified on the basis of the scientific method -- a method which presumes that there is an OBJECTIVE reality which exists for all observers. (Yes, as we have learned more, we find that some things we would have thought were parts of that objective reality are not, while other things we never had guessed existed appear to be parts of it. At some basic level, though, there is still assumed to be an objective reality.) There is a serious problem with trying to use quantum mechanics as the means by which an observer creates the reality that contains quantum mechanics (to say nothing of himself!).

Thirdly, it appears that most of the universe is AT BEST indirectly observable by intelligent corporeal life. This is true whether we are talking about "per unit volume" or "per unit mass-energy". It is probably also true regarding time: we know of no corporeal life more than a few billion years old, and for the first billion years or so the universe would have been incapable of supporting life as we know it.

I recently read a book with much more interesting things to say on a similar topic, Russell Standish's Theory of Nothing. I wouldn't claim to believe the ideas in the book. I'd classify the ideas as scientifically plausible and science fictionally way cool. Some of them make testable predictions, too -- that's always the best way to avoid falling into pseudoscientific thinking.

Interesting relativistic complication: it's not just that light has a certain speed, it's that the speed of light is the speed at which causation propogates through space. If the sun winked out of existence, both the sun's light and that moment that it winked out of existence would take 8 minutes to get to us. There's fundamentally an eight-minute gap between the instantaneous "now" at the sun and the instantaneous "now" at the earth. For any timespan shorter than 8 minutes, the sun and the earth are virtually in different universes. It's only timespans longer than 8 minutes that encompass both the earth and the sun.

When an argument devolves to debating the meaning of a word, treating that as though it makes any difference to anything, then it has lost all relation to reality. In such a case the only solution is to reframe the argument in more specific terminology.

As for the "real" meaning of words, see 37 Ways That Words Can Be Wrong

When the one says "yes" and the other says "no" to the question of the sound of a tree falling in an uninhabited forest, they are not disagreeing over anything that exists in the real world . . . .

But in the real world, there is a difference between a tree falling in the forest with no one there, and a tree falling in the forest with someone there anatomically and physiologically capable of hearing.

. . . . they are only disagreeing over what the word "sound" means

So? Are you saying there is no room for disagreement about what is meant by sound? And isn't it very much the job of philosophy to raise questions about what is really meant by words like sound and whether or not they are fuzzy or ambiguous?

When the one says "yes" and the other says "no" to the question of the sound of a tree falling in an uninhabited forest, they are not disagreeing over anything that exists in the real world, they are only disagreeing over what the word "sound" means.

Likewise, colour is a related set of concepts which normally correspond closely enough to each other that we don't have to sweat the fine differences in most contexts. But there is no point in trying to play definitional games with it; if you want to draw finer distinctions, then use more specific terminology rather than trying to artificially limit the usage of existing words.