Players can get faster in a college S&C program but probably not nearly to the degree that they can get stronger. Acceleration is the same, IMO -- increasing it is rather difficult bc its mostly developed by the late teens and is as much genetics as conditioning for those who are already well condition (as a highly sought HS WR should be). Also, while players can develop their speed and acceleration on the margin in college, it's a relative scenario. In other words, most skill position players will improve their speed and acceleration (on the margin) in college. It would take a poorly developed (nutrition, speed & weight training) prospect to see a dramatic increase in speed and acceleration relative to peers.
*One exception to this is if a player is taking something that unnaturally gives him a boast, such as steroids, testosterone, etc.
Translating this to KD Nixon, I don't see him having the speed necessary to make up for his lack of height. His build is actually bigger than most receivers also (which is why he's been described as looking like a RB). In this regard, he's nothing at all like McCluster -- not in build, speed, acceleration, or shiftiness. McCluster had elite acceleration, speed, and shiftiness. I don't see KD having elite speed or acceleration (not as sure on shiftiness but I have my doubts). Height might be the only similarity between the two that I can see.
KD has shown the ability to get separation at the 5-Star Challenge, but that was in a 7-on-7 setting with limited ability for CBs to jam at the LOS. He did display excellent hands and I think he'll do well in a less physical conference. As I expressed before, however, I don't see him being a difference maker in the SEC. Not enough speed or size to be a consistent threat. He'd also be a hard target for a QB to hit beyond 5 or 10 yards downfield, especially in the middle of the field, which is where a slot receiver often does much of his damage.
Ironically, he's one of our highest rated players based on his composite ranking, yet I think he's one of the players we most need to let go. Just my opinion. If he signs with UT then I hope I'm wrong. I'm sure he's got a chip on his shoulder from hearing this very type of analysis before.