I see this from two points of view... having the high name recognition of John Mayer associated with PRS; and, PRS as a brand, what it is know for.
The first point is for PRS the company - high visibility, able to meet the very specific needs of a high profile artist and drive more PRS sales. The world needs another guitar hero, and while Mayer might not be a guitar hero in the true sense, he certainly has a high profile across several genres, which is a marketing dream for PRS. That's the "duh" part - of course PRS would jump all over this opportunity to work with him!
But from the PRS "brand" perspective, IMO, PRS doesn't
need to be copying other well established/iconic guitars. If Brad Paisley came along, would we be looking at a PRS T-style guitar? At this point, PRSi pretty much have instant recognition - you know a PRS when you see one. On the other hand, a high-end brand like Suhr or Tom Anderson base their guitars on the iconic originals, and produce incredible versions of those. But, most people probably couldn't pick out a Suhr or Anderson in a lineup if they didn't see the headstocks. Again, my opinion, PRS could have stopped at the JM amp and Modern Eagle. Heck, Santana has been on PRS's roster for 30 years and that guitar is still going strong. I have other opinions, but I'll stop here.