Was the irony intentional? If not that is just priceless!
Humans being what they are, when they define things it will inevitably tend to influence what predictions they make. Where a boundedly rational agent prescribed a terrible definition would be merely less efficient a human will also end up with biased predictions when reasoning from the prediction. Also, as you note, declaring a definition can sometimes imply that a prediction is likely to be made that the definition matches the mental concept while also carving reality effectively at it's joints.
The above being the case definitions can and should be dismissed as wrong. This is definitely related to the predictions that accompany them. This is approximately a representation of the non-verbal reasoning that flashed through my mind prompting my own rejection of the 'self as future folks you care about and can influence' definition. It is also what flashes through my mind when I reject why I must reject any definition of 'define' and 'predict' which doesn't keep the two words distinct. Just because 'human' is closely related to 'featherless biped' it doesn't mean they are the same thing!
I suppose this must be my mental concept of what we're doing when defining a term like "self", which is what impels me to use "define" and "predict" in similar ways.
Just so long as you don't mind if you mislabel a whole lot of plucked chickens.
Understanding the various relationships between definitions and predictions is critical for anyone trying to engage in useful philosophy. But it isn't helpful just to mush the two concepts together. Instead we can let our understanding the predictions involved govern how we go about proposing and using definitions.
Eliezer wonders about the thread of conscious experience: "I don't think that, if I were really selfish, I could jump off a cliff knowing smugly that a different person would experience the consequence of hitting the ground."
Instead of wondering whether we should be selfish towards our future selves, let's reverse the question. Let's define our future selves as agents that we can strongly influence, and that we strongly care about. There are other aspects that round out our intuitive idea of future selves (such as having the same name and possessions, and a thread of conscious experience), but this seems the most fundamental one.
In future, this may help clarify issues of personal identity once copying is widespread:
These two future copies, Mr. Jones, are they both 'you'? "Well yes, I care about both, and can influence them both."
Mr Jones Alpha, do you feel that Mr Jones Beta, the other current copy, is 'you'? "Well no, I only care a bit about him, and have little control over his actions."
Mr Evolutionary-Jones Alpha, do you feel that Mr Evolutionary-Jones Beta, the other current copy, is 'you'? "To some extent; I care strongly about him, but I only control his actions in an updateless way."
Mr Instant-Hedonist-Jones, how long have you lived? "Well, I don't care about myself in the past or in the future, beyond my current single conscious experience. So I'd say I've lived a few seconds, a minute at most. The other Mr Instant-Hedonist-Jones are strangers to me; do with them what you will. Though I can still influence them strongly, I suppose; tell you what, I'll sell my future self into slavery for a nice ice-cream. Delivered right now."