Okay, this may be me reading way too much into it, but Ellie "mentions" Ish here
. It's probably a coincidence but it's been bugging me because it's phrased in a very weird way. She says "Don't worry, I've done this before." and that would be enough, but she feels the need to reinforce that: "I'm kind of an expert...-ish".
That kind of reiteration would feel right if she were referencing some other instance of her stitching someone up that the player has seen. She dwells on it for just a second too long.
But more importantly, "I'm an expert-ish?". Normally someone would say "I'm kind of an expert...maybe" or "...sorta".
Plus, look at how it's formatted: "I'm kind of an expert..." "-ish." The hyphen. Ish signs all his notes as "-ISH".
Again, this is probably nothing, but then again people have been clamoring for some Ish-related DLC ever since story DLC was announced. Or maybe they're just trolling.