Of course, "this guy kind of looks like this thing" isn't much of a basis for a firm theory. However, there's another tidbit nestled in the Visual Dictionary that, combined with speculation about the plot of The Last Jedi based on marketing, gives it a little more weight: Snoke wants Ben Solo, aka Kylo Ren, because he believes that only someone from the Skywalker line can destroy the last Jedi (that is, Luke). If, as marketing seems to hint, Rey falls to the Dark Side while Ben redeems himself, and if Luke dies, that would then make Snoke the true last Jedi. A Skywalker (that is, Ben Solo) would be the only one able to destroy him. In fact, if Snoke truly believes only a Skywalker can destroy the last Jedi, his attempts to kill Luke may be to rid the galaxy of Skywalkers, not Jedi, thus protecting himself as the true last Jedi.
Why, then, if Snoke is the Prime Jedi, has he never looked in the first Jedi temple, where Luke has been in hiding? Being thousands of years old, he may have simply forgotten its location, but another theory presents itself, based on his scenes in The Force Awakens. It's interesting to note that Snoke isn't interested in hunting Luke, but rather preventing the Resistance from reaching him. His greatest concern seems to be preventing the rise of the "New Jedi." General Hux is perfectly willing to see BB-8 and the map destroyed, rather than captured, and Snoke's orders, upon learning that the Resistance has the map, is to prevent the Resistance from reaching Luke, rather than reaching Luke first. That raises the important question of what Snoke's true motivations are, which will hopefully be answered in The Last Jedi.
If Snoke is in fact the Prime Jedi, or at the very least a very early Jedi, he could be a hard-line traditionalist. The mosaic on Ahch-To depicts the Prime Jedi in a yin-yang-ish balance symbol, implying the early members of the Order were concerned with the balance between the dark and the light. That in turn plays into the conflict between Luke and Snoke: Luke is pure light, so Snoke becomes pure dark to provide the necessary balance. By destroying Luke, Snoke could return to his original, balanced state. Of course, that interpretation runs directly counter to George Lucas' original concept of the Force, i.e. the Dark Side is the unbalancing factor, and "bringing balance to the Force," as Anakin Skywalker was prophesied to do, means removing the influence of the Dark Side.
There's also the seemingly obvious tidbit describing the Prime Jedi as the first of the Order, which certainly evokes the First Order. The First Order also certainly implies Snoke is setting himself up in direct opposition to the Jedi Order, possibly seeking to reestablish the First Jedi Order. Kylo Ren's lightsaber, revealed in Star Wars Rebels to be a model of lightsaber from thousands of years before the movies, also points to his age being "really dang old."
Written and directed by Rian Johnson, Star Wars: The Last Jedi stars Mark Hamill as Luke Skywalker, Daisy Ridley as Rey, John Boyega as Finn, Adam Driver as Kylo Ren, Oscar Isaac as Poe Dameron, Andy Serkis as Supreme Leader Snoke, Domhnall Gleeson as General Hux, Gwendoline Christie as Captain Phasma, Anthony Daniels as C-3PO, Lupita Nyong’o as Maz Kanata, Benicio Del Toro as ‘DJ’, Kelly Marie Tran as Rose Tico, Laura Dern as Vice Admiral Amilyn Holdo, and the late Carrie Fisher as General Leia Organa. The film opens worldwide Friday, Dec. 15.