As for my answer to the question, Jones has got to be a DB primarily.
He has ball-skills, instincts, and physicality that is rare. You need that guy flying around making plays defensively because they're hard to find.
Yes, he is undersized but he actually has really, really good technique on the perimeter, tracks/plays the ball well. He isn't just a slot CB IMO - the guy can play inside or outside, and he could probably play S very well, too. He's had a few really damn good tackles/hits, and not only on smaller players; he is fearless and brings the wood against bigger guys (absolutely crushed one of the Bengals' TEs on a flat route the other day).
The only real limitation I see is his height/length, that's it. If Jones was 2-3 inches taller, he absolutely would've been a top-5, first-round pick. Special player from what I've seen.
Now, with all of that said, I would argue that Jones is also one of the best (if not the best) offensive weapon on the team. He has short-area quickness, the ability to start/stop, change direction, and accelerate in very small spaces. There is not a single other offensive player on the team currently who is anywhere near him in those regards, not even close. He brings a skill-set and ability to the offensive side of the ball that is also desperately needed. It's no surprise that pretty much every time he's touched the ball offensively (generally on screens near the LOS) he's made plays basically every time, and provided a glimpse of something we haven't seen in a long time. They haven't had a receiver with his short-area quickness since Welker (although Jones is much faster in a straight line).
So, piggybacking off of that, what they should do (IMHO) is play Jones at DB because he possesses toughness, physicality, instincts, and ball-skills that are special, but use Jones' athletic profile when looking for offensive weapons, particularly slot receivers, 3rd-down backs, gadget guys, etc.