I've just seen Matpat's game theory on melee attacks in Halo. The request for anyone who can convince him to try his hand at Marathon and Pathways theories is still open.
Once again, I'd do it myself but I don't use the same social sites as Mat, nor do I have a Youtube account. I think his theory on the canon like Infinity's events and how the fan mods fit in, or anything similar like why System Shock draws so many parallels with PID and Marathon canon-wise would help rise it from obscurity and get more people interested.
Maybe he can find evidence in some areas where others like myself haven't.
Maybe a theory on Marathon and Halo being so similar in places? (Eternal being partially related to Halo's early Alpha as an example)
Theories for PID might work too, like the Muller mystery or what the names of the bosses represent e.g. Greed the blue meanie, Wrk Doubt in Infinity, The PID W'rk's dream avatar from OKWEWS. (I forget the name)