To pluto actually isn't that different in meaning from the verb to plateau, but while to plateau means to maintain the same level of achievement, weight, etc, to pluto means gradually to lose importance.
But to which pluto does it refer? you may ask. And it would be a reasonable question because all of them are, sadly, pluto-ing. (I think that must be how you spell it. Plutoing looks just wrong.)
Consider: there are far fewer worshippers of the god Pluto than there used to be; many cartoon animations have risen up to challenge the dog Pluto's status in the affection of the children of the world; and then there's the planet. Or, actually, there isn't the planet, because Pluto, poor Pluto, isn't a planet any more.
And who doesn't feel sad and wistfully nostalgic about that?
It is said that every political career ends in failure. Well, I suppose that for all of us it's either failure or going out with a bang, so there are worse things than pluto-ing.
But, hey. Let's not do either today, eh?
Thing Not To Do Today: pluto. Pluto the god, after whom the other plutos are named, may originally have meant rich father because he was the ruler of the underworld from whence gold, diamonds, and germinating seeds come.