It really isn't that great in M+, unless if your entire group plays around the fact that you are a sub rogue. Secret Technique needs to deal more damage, specifically on the main target (which is suppose to be sub's "niche"). There is a reason why there are far more assassination rogues in M+ compared to sub rogues. You can still do very good damage without the group playing around you and even in those perfect scenarios for sub, it isn't that much better than assassination. Why put a ton of more effort when the results are almost the same?
Yes, you can play sub right now in M+. But it is definitely gonna be weaker in 8.1 unless if blizz buffs Secret technique damage or give a very large buff to shuriken storm itself.