I think the following would need to occur for Mitchell to be viewed as surpassing Stockton and Malone (not necessarily in order of importance):
1) Longevity with the franchise. At least 10 years, and ending his career here is best.
2) Popularity. He is already mostly on par with Stock and Malone, and ahead of them in this regard in lots of ways. He is far more likable than either Stock or Malone really ever were. Stock was too stoic, Malone too, idk, full of himself maybe? Malone was at least an entertaining interview, Stock was a good all around guy that just didn't say much. Mitchell has that positive outlook and cares about the community and that goes a long way.
3) High level of personal performance. Not expecting him to beat the stats that Stock and Malone put up, both of Stock's records are going to be damn near impossible to repeat let along beat, and it is a bit much to ask for Mitchell to be the 2nd leading scorer in league history. But he need to put up solid numbers across the board, and do it consistently. A consistent 22 ppg, maybe higher (Malone averaged 25 ppg for this career), 4 asst, 4 boards, 2 steals, etc. This is a combination of single game/single season/career stats.
4) Win - regular season. Has to carry us to multiple winning seasons, threatening the top teams in the league for regular season wins. Needs to top 60 wins a few times.
5) Win - playoffs. Has to lead the team to multiple playoff appearances, with many series wins. Needs to make the conference finals a few times. Needs to be the decisive playoff leader in this pursuit. Good news is he has one season of this under his belt already.
6) Win - championship? If he wins one, and that is all he does, say in year 5, and has #2 on this list wrapped up, and the very next year bolts for another super-team, where would he fall? Would the ring be enough to surpass Stock and Malone? Personally I don't think so. It puts him solidly in 3rd place on the all-time Jazz list with this achievement alone, but he needs a couple more on this list to really surpass the statues and get his own. It would be enough to get a jersey retired definitely, but not a statue.
So right now, in comparison to Stock and Malone, I give him this rating, point by point on the list above:
Completely arbitrary rating scale:
-3 = solidly behind stock and malone
-1 = gaining ground, pretty close, but still behind
0 = on par or not applicable (yet)
+1 = a bit ahead
+3 = well ahead of the statues
#1: -3
#2: 0
#3: -3
#4: -1 (giving him credit for nearly single-handedly turning around what should have been one of our worst seasons)
#5: -3
#6: 0
Total score = -10
Score needed to match Malone and Stockton = -2 to 3
Score needed to "surpass" Malone and Stockton (probably enough for the statue) = 6-12 (and no more than 1 negative category, 0 is ok)
Score needed to become the Jazz Legend of ancient mythology = 15+ (no negative categories, no more than 1 @ 0)
(scores of 4, 5, 13, and 14 are somewhat ambiguous depending on the number of negative categories)