This is kind of my overall theory of how Barry will get back his speed. None of this is confirmed and after all, this is just my idea.
So Barry is running out of speed as we may know it and he's already created a beta version of Gideon that could use some improvement. Team Flash is already working on an artificial speed force that I'm sure will work, but how will Barry access it? Doesn't he need speed which he lacks? Well here is the solution to Barry's problem. He has to become Savitar.
Well, no, not Savitar 100% but I think he may need to create the Savitar suit so that he can save his speed, since the suit (in season 3) basically made Barry faster so that's what Barry may need.
He also might need the savitar suit in case there is any risk of dying in the artificial speed force. It would keep him safe the entire time. Or maybe a Speed Force Bazooka will be needed and would have to be shot in the Artificial Speed Force (ASF)? Who knows.
So what are your guys' theories? How do you think Barry will get his Speed back? Once its fixed, will we see Bart Allen like teased in season 3? I think the events that happened in season 3 may pop back up again in season 4.