I don't know, I kinda enjoy the way they are now. Initially, the only reason I (or anyone else that I know) would buy Boots of Mobility over the other options is if I wanted to get around the map faster, usually as a jungler. I didn't buy them to give me an edge in battle (you lose the ms buff upon taking dmg anyway), I simply wanted the bonus mobility.
That being said, they were a little overpriced for what they offered in comparison to the other boots. If I wanted to catch and keep up with targets in fights, then BoS worked better. The higher movespeed compared to the rest of the boots was decent, gave slow reduction, and I could maintain the speed after making contact with that one annoying minion. Most of the time I built mobi boots, I ended up selling them later anyway for the defensive stats offered by Tabi or Merc treads.
The new mobi boots serve their purpose much better for me. Cost efficient comute. With the lowered price, I can buy them much earlier without getting too far behind item-wise and get the same travel time as before. The lowered in-fight movespeed alteration is barely noticeable, and I still end up selling them late game when I already have more than enough gold for better team-fight beneficial boots.
That's just my opinion though.
TL;DR Cheaper mobility, lowered ms in-fight barely noticeable