I suppose I will be the minority here . I am not a Shang main, but I play him. I've played a little bit of all of the cast. I've never had a problem with reptile players as Shang, or at least I've never felt like it was an uneven match. I was wanting to post this thread myself.
On paper, shang has skulls which occupy space and spot every forward special of reptiles aside from EX slide. You throw out a straight skull, then you get a mix up between upskull over their head or upskull in front of them. Reptiles projectiles are slow if you can avoid the spit, so unlike most characters Reptile should not give shang tsung a hard time from full screen.
Up close it is just who starts the pressure first, it seems 5-5 to me. F4 GS is 10 frames on start up and +2 on block. Reptiles fastest poke is 8 frames. If reptile is player 2, that is a just-frame block infinite. If he is player 1 it is still going to be hella hard to poke out. His only way out of pressure is to dash, so that is a guessing game. If you block it, he is technically at -15. If you're blocking right there, you read the dash. You should be ready to punish with F434.
It's 5-5 imo, but I would not be shocked if it was in shang's favor. Of course, I am a noob. I would love to hear Detroit's opinion on this match up.
AT THE VERY LEAST this match up requires reptile to approach it differently than most of his matchups