Reasons to deny Gaster relevance to the plot:

Ok, you, crazy paranodiacs of r/deltarune, listen, because I won't repeat it:

  1. "Interesting" words

"Interesting" and "very" are words in the english dictionary, saying it doesn't make you gaster/gaster related

The entry number 17 is an unused/only code content from undertale, so it isn't an "evidence" of nothing

  1. Is an easter egg from other game

Toby Fox can make a reference of another game, and that doesn't make both games related, or do you think that Dr.Andonuts (that blue cat from earthbound) is Sans because the megalovania song plays in both fights?

  1. It would be a "only PC"

If you don't know who Gaster is, the intro guy could be even Toby Fox itself, and a console player hasn't any way to know about him (supposing that they don't play Undertale 100 times or buying it again on PC for no reason)

  1. The toby fox social media "show"

Also, if you pick the game after toby fox making all the show with the newsletters (for example, 1 year after chapter 7 is released) you won't understad anything, if the newsletter easter eggs are plot-related.

  1. "Garbage noise"

Apart from being in the ,again, unused entry number 17 from undertale, is easy to recycle as a laggy and trash noise, so I think that Tony Fox simply thought: "Oh look I already have a trashy noise to use"

  1. Casual players

Even if you play on PC, a normal person doesn't look in the game files like a deranged man

If you played all undertale/deltarune in a row (1st time) you wouldn't know all the info from the game files, and you wouldn't look in reddit or youtube for info about an easter egg that 1. you don't know that exists, 2.Even if you know, why would you take the risk to spoil yourself?

I don't think that Toby Fox will make such a convoluted plot, only to make half or more of the player don't understanding it

Conclusion: I'm not denying the Gaster existence as an easter egg, but having relevance to the plot, at least with the info that we have, is just pipe-dreaming

And not, Toby Foz is not any kind of foreshadowing god, so he hasn't all the plot complete, if he had, he would release deltarune complete, instead of fractioned