Yes, Midak. Our favorite eccentric Onu-Matoran who just loves spending his days in the sunlight, unlike his underground friends.
You might strike this little quirk of his as just it, a quirk of personality. And he also displayed the same properties as the rest of Onu-Matoran (at least according to Biosector), unlike Takua.
But on the other hand, did we see a lot of eccentric matoran from other tribes like Midak? I don't think so. You can say Krakua, but he was destined to become a Toa. Was Midak destined? We'll never know. But as far as we know, no, he did not.
Also, it was never stated how many Matoran of Light has been sent to Metru Nui during the Time Slip, so it's safe to assume that it may have not been just one - Takua. Both of them displayed behaviors not typical to their respective adoptive tribes (with Takua being more of an oddball than Midak).
So, given his unusual attraction to the light, and overall eccentricity, I ask: do you think it is a plausible theory? Do you think Midak would fit the "amnesiac Av-Matoran" bill?
Several of my friends have found this idea to be very compelling.