You see flash only as an "free escape route". You can make play with flash, save life, fail flash, waste it, and more.
Here's some points(to keep flash) :
-Low mobility champs need some kind of escape or get buffed (add number to their kits, add CC, etc.) : I won't play a champions withtout escape if flash is removed (Malazhar for instance would get ganked no stop.)
-High mobility on champions kits is more present than ever before : Really, look at almost all the last champs release, they come with CC and high mobility skills.
-Aggressive play : If flash is removed, there would be less aggressive play, league would become a more passive game. Maybe it won't matter in lower elo, but in high elo, when flash is down, people play more safe and then nothing happen.
I can find more reasons if you want.
I have some exemple of nice play with Flash :
-Flashing to save a teamate from Caitlyn's ult.
-Maokai jumping on you, you flash underturret (or near your teamate)
-Flash juke (You go near a wall to bait the enemy flash/abilities, there's more juke with flash)
-Malphite ulting you, you flash at the last moment to dodge it.
-You flash over Ashe's arrow.
-You're ulting as fiddle(Kennen, amumu, or anyone with AOE), you flash to reach the enemy team.
-Shen's taunt + flash combo.
-You go really aggressive and got caught, you flash out.
Overall, i see more play possible because we have flash.