Okay so you are asking something entirely different with your title than you are discussing in the post.
To answer the title, yes there is a reason to pick Shyvana. The problem is that niche is too spread out among multiple champions, being the job of outpunching anybody that walks by for the most part. Her old passive, her Q, and her E serve no other purpose than for fighting or maybe destroying towers depending on her build with her Q. On top of this, her W is offensive waveclear and long term mobility. If not for her Ultimate or new Passive, there is literally nothing in Shyvana's identity that isn't "statchecking splitpusher". To add on to this, her Ultimate isn't even that great when compared to say, Malphite. Her only real identity right now is in her Dragon passive, putting her in a similar category to the likes of Nunu and Skarner as a neutral objective controller which works "okay" with her splitpushing basic kit. Ideally, her niche should be getting the most bang for your buck with dragon control while transitioning into a ridiculous splitpusher. Realistically, you will basically never pick her unless she is stronger than most other splitpushers in the game.
You don't pick Shyvana to gank. Hell, I'd say you pick Shyvana with a great big neon sign for the enemy team that says "I will not gank". With that in mind, the movement speed boost seems to target the wrong area. You're not defining a niche for Shyvana this way, you're just giving her more generalist power so now she's the splitpushing neutral objective champion that also has just that much more ganking potential. Buffing her splitpushing power is also not a real option if the goal is defining a niche for her. If you really want a better niche for her, look at her passive or giving her kit a new functionality other than "walking statstick" and "piss Malphite Ult"