I think he's definitely a compelling buy low target. If you look at what happened last offseason, the unheralded sophomore backs ended up being much better values than the hyped guys. Charles, Rice, Mendenhall, and Felix were all available in the middle rounds of most dynasty startups whereas Johnson, Forte, and Slaton were all top 15 picks in most leagues. The unheralded backs weren't any less talented than Johnson/Slaton/Forte. They were just less expensive because the awareness of their talent was lower (because they hadn't played much).
The same thing is happening this season. The rookie backs who got a lot of playing time are becoming overvalued (Moreno, Wells, Greene). The guys who didn't play much or didn't finish strong are getting overlooked a little bit (Brown, McCoy). I think the latter group offers a more intriguing risk/reward proposition and I'll definitely be looking into possibly acquiring those two guys in some of my leagues if the price is decent.
I see a lot of parallels between McCoy and Ray Rice. Both were late second round picks. Both played reasonably well as rookies, but received limited hype because a gimmicky fullback stole some of their carries and a mediocre veteran threatened to do the same. This situation is a lot better than it looks on paper. Westbrook looks done and Weaver will never be more than a gimmick like McClain. McCoy is the obvious heir to the starting job here and it's unlikely that Philadelphia will be able to draft anyone better than him this year (there are maybe only 4-5 backs in this draft class who look like they could threaten him).
Is McCoy as good as Rice? I doubt it. Rice is pretty special. Great power, fluid hips, and lots of explosion. I don't think McCoy has the potential to be that good, but he's not exactly chopped liver. He has the dynamic lateral quickness that you want in a pro back. He's a good receiver. He looks like he has added enough weight to be an every down guy in Philly's system. Most importantly, he was pretty productive this season when given 10+ carries. Here's his game log when he got significant touches:
20 carries for 84 yards (4.2 YPC), 1 catch for 9 yards
14 carries for 37 yards (2.6 YPC), 5 catches for 30 yards
11 carries for 82 yards (7.5 YPC), 2 catches for 10 yards
13 carries for 54 yards (4.2 YPC), 5 catches for 61 yards
20 carries for 99 yards (5.0 YPC), no catches
17 carries for 76 yards (4.5 YPC), 4 catches for 25 yards
10 carries for 28 yards (2.8 YPC), 4 catches for 26 yards
Not bad. Five good games and only two duds. In the three games where he got 15+ carries, he averaged 4.5 YPC.
I don't see any reason why can't make a value jump next year like Charles and Rice did this season. It's not a guarantee, but he certainly has the potential and his current price probably isn't sky high in most leagues. As this thread demonstrates, a lot of people are placing too much emphasis on the short term situation (just as they did with Rice last year).