This is completely stupid imo, not to be harsh or anything (ok, I probably failed trying to make this not harsh), but osu! was made for just 2 keys, and adding an extra (or more) keys really completely changes the game (and also makes a shit load of things a shit ton easier). If you reasoning to add a third key is because you aren't good enough, I honestly think you shouldn't even bother asking. It's like asking, "God, can I have a third arm so I can play piano better?" Well, if you get rid of the logical outcome of probably looking disgusting and ugly with a third arm, having a third really does help a lot for piano. It doesn't make sense, and also you will never get a third arm since you were made to only have two arms, as osu! was made for only two keys.
Maybe not the best analogy, but anyways, if you think you seriously reached your limitations and cannot even come close to streaming as well as TTTL or something, go practice other things like accuracy and jumps, and be super pro at those. But you'd be surprised at what one can accomplish if you just sit down and try. I could barely stream 200BPM before, but I have gotten much further now. I still suck at streaming, but I don't think I have reached my limitations yet and I just practice to reach up there instead of trying to find an easier way out.