The game is being reworked and Nyx is still playing around with John's Tattoos, at some pictures they look like this:
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This one looks like a better match for the Melissa dream guy, but i wouldn't put much stock on tattoo matching since these things are still in flux.
In my opinion there's so much suggestion it's John that it would be kinda lame to pull a different guy who fits the description perfectly, just for a "you thought it was John, but Erynn's dad is actually his cousin/brother (who we never heard about before)".
If we do a count:
He fits the decription(tall, blonde and tattoed).
Looking at Erynn immediately brings some memories of someone he knew (you are gonna make that just upon gazing at Erynn he immediately thinks about a girl his brother/cousin fucked 20 years ago? That's justifiable for an uber hot girl you fucked... but way more difficult for someone else's girl).
Erynn herself thinking "this guy is the perfect match of what mom told me" upon looking at him.
And the constant... Erynn and Iris are so much like each other... they look like they could be sisters.
Erynn also knows his first name of her father and that didn't stop her thinking this could be her dad.
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While i'm sure Nyx(not just her, most devs) would love to pull this type of gotcha and surprise players, they shouldn't do that at the expense of a good story.
A new guy would be meaningless, John as Erynn's dad will be emotional.