I personally see no NHL future for him: at least not here. This is an internet message board so hyperbole is the name of the game. Of course, my 100% guarantee means nothing except to emphatically state that I personally don't believe he will amount to much at the NHL level, if anything at all.
I stated for years and years that no team that picked up Dany Heatley would ever win a Cup because he was a curse. No scouting involved in that but I probably guaranteed that as well, which is to say I may be pretty adamant about something based on little evidence other than my gut feeling. With Rempal, I've seen enough to not be impressed. When combined with his age and how things generally go for players of his size/skill/career path to date, it is enough for me to feel confident he won't make an impact.
As for Wagner, I understand where you are coming from because Regulate believed he wasn't ready so you score points there. Since we are talking about how I feel, I've always been high on Wagner and he differs from Rempal in a giant way: he has an absolutely elite skill + good size whereas Rempal doesn't possess anything of the elite variety. Regulate isn't wrong to say Wagner needed--or still needs--more seasoning to round out his game in the defensive zone but being in the discussion for fastest player in the league is going to get you some NHL playing time.
Rempal would be useless on the bottom lines so he'll need to be a Top 6. That would be a tall order for him to do. Not having an impact camp is pretty detrimental to him, as was goose-egging in his seven games last year and then not getting any more tastes of the NHL in a lost season when everyone else of worth from Ontario was coming up. I mean, I'm pretty sure he was getting healthy scratched.
All that being said, he could have a huge season down there and prove me wrong. Hope he does. I just don't see it. If he winds up being a thing, I'll eat crow and everyone on here can say "I told you so". If I'm right, I won't say "I told you so" though because I don't think I'm going out on much of a limb here.