Peter's scar that Future Peter has on his face is going to be related to Peter
fighting his dad. Think about it - he had Claire's regeneration ability, so
the only way that Peter could get scarred facially is if he didn't have that
power. It just so happens he's in that very predicament right now, so look
for the battle that brings about that wicked scar to happen sometime
soon.
Ummmm...wow? Kinda scary I also nailed how Arthur would be the one to give Peter that scar. Hey, some theories are easy to predict - like Elle not lasting too much longer since Kristen Bell was still being mentioned as a "special guest star" and not one of the main cast - others take guts and a keen sense of insight to make. Too bad I wasn't able to predict the Haitian's power could be overcome by a more powerful person (in this case, Arthur). I also couldn't have predicted that the Haitian's power would stop working altogether as a result of being overcome by Arthur, thus allowing Sylar to use his own powers. So, the Haitian's ability just stopped working just like that? Sure, he was mentally spent but I already pointed out he doesn't need to be concentrating for his ability to work, as evidenced by Parkman's power not working in Primatech and when Hiro was trying to steal the formula back and the Haitian was in the in the movie theater; it took Hiro and Ando combined to beat him by ambushing him since Hiro's power wasn't working around the Haitian.
One thing that sucks about Peter being scarred is now for the rest of the series Milo V. will have to wear that scar on his face. And how the hell are we gonna tell the difference between Future Peter and Present Peter now! OMG!
Note (updated 12/11): A reader of the site keenly pointed out that the scar that Peter aquired in this latest episode is not the same scar that Future Peter has. For reference, check out the massive Future Peter scar:
My bigger overall point is this (and I'm glad the reader who made the comment allowed me to flesh out my thoughts) - how many more times is Peter going to be without his powers? How many more times in this series future will Peter not have the ability to regenerate himself? As soon as he gets his power back (even if it's just his power absorbtion ability) he's going to run into someone who can regenerate (most likely Claire) so it's safe to say Peter will always have the regen ability in one form or another. How many more times can the writers go to that plot device where Peter is powerless? The answer to this question is "not likely to happen many more times, if at all". I think this will be the only time Peter is without his powers, thus making this the only time he could be scarred and not heal himself. Furthermore I think this will be the scar that Future Peter displays. Again, thanks to the person who commented on this to begin with. I look forward to the people who point out things I may have overlooked and I look forward to seeing if I was ultimately right or wrong.