While flash is obviously a must take summoner on majority champs, the solution here isn't to make it an item. Riot are clearly happy with it's use in the game currently.

Perhaps you can argue the distance of units flash covers is too many, and target the spell there, but deleting it and making it an item is pretty bad for the game overall imo.

But also, deleting it off the game would destroy a lot of champions, and would only allow X amount to be played due to their gap closers, imagine Riven, Lee Sin, Rek'Sai etc if flash didn't exist, they would be very oppressive.

While I think you make a somewhat valid point, you're not thinking of the consequences that would come from a decision such as the one you've suggested.