Let's say for the sake of argument, SE keeps "removing" gears/emotes/whatevers from the in game drops/achievements/quests, then the value of your sub diminishes, and eventually you and other people will feel that the sub fee is no longer worth it, and leave the game. In that case SE will have to reevaluate what they should put in the base game to keep players subbed. You only need to evaluate the value of your sub fee against what's offered in the base game (excluding mogstation stuffs), if you think it's no longer worth it for you then the best thing for you to do would be unsubbing and finding a different game.

The fact that SE keeps adding those stuffs on mogstation means that it's profitable (many people buy them) while not really harming the number of subs (many people think what they get from the base game is still worth the sub fee). Will SE eventually go "too far" and put too many things on the mogstation while leaving the base game lacking? Maybe. Maybe not.