Sorry I’m late.
As discussed at length on discord, Sparkle Tokens, while initially distributed for a limited time during the HC celebrating their release, have had several more copies sold off during every auction since. While Andy has mentioned there will not be as high as 3 per auction, it has also been mentioned that they will be likely returning next anniversary HC.
I do not think adding more sparkle tokens into the game is a good idea. So long as the sparkle token is available, the rarest shiny can be no rarer than the sparkle token. Had the token been more limited in what it could be used on–such as say, it being only usable on your starter–then I do not believe this would have been a problem. But as they say, hindsight is 20/20, and limiting the token now would be a slap in the face to everyone who invested in them.
To avoid worsening the impact the token already has on existing rarer shiny pokemon, as well as the rarity of shiny pokemon implemented in the future, I believe the best course of action is to either discontinue it, or heavily reduce the rate at which they enter the game. An alternative auction item could be having your starter made shiny; this is something that cannot be held in a sort of “superposition” like the sparkle token can–allowing the player to use it whenever the player pleases on whatever they please, which I believe to be harmful to the rarity of shiny specific shiny pokemon that would otherwise be comparably difficult to obtain.