There are multiple problems with the whole Judas thing. First you have to consider all the alternate versions of the story where Judas did not betray Jesus, but rather was instructed by him to turn him in so that everything would be accomplished. Second, there is a very real possibility that Judas never existed at all, and his character is a personification of the nation of Judah. Clearly Judah betrayed their god on that day, when they joined the pagans in having him crucified.

Now let's go over the idea that Judas "repented". It is not quite true that this is the correct term. "repent" is μετανοεειν (to change mind), but it says Judas μεταμεληθεις (changed concern). These words are very similar, but the subtle difference could imply that Judas only regretted his actions due to the consequences, not because he had a change of heart. As in "you'll be sorry when you receive your punishment". This is the kind of nuance that's lost in translation.

1 John 1:9 indeed does not say repent and be forgiven. However, the verse by itself is even more permissive. It says all it takes is admitting that you have some. Did Judas do that? No, he ran off and killed himself. He never sought redemption, he just condemned himself. This is why the "I don't deserve mercy" attitude is so dangerous, because it will likely make you refuse it like Judas. This can actually be rooted in pride: "I'm too good to let someone else pay my debts!".

The only thing ever suggested as "beyond forgiveness" is slandering the holy spirit. That was only ever addressed when some smug Pharisees were accusing Jesus of performing miracles through the king of demons, who clearly had no remorse at all. So it's unclear how unforgivable it is, ie. actual repentance may still clear the charge if you stop committing it.