Can Summoner Spell cooldowns for both teams be visible through Tab?
I feel that that the best counter for Flash is to continue aggression while Flash is on cooldown. However, during that 5 minute CD, it's easy to forget how long ago flash was used and if it is on CD. Especially at low levels and I even think this is the case in tournament play. The game has a lot of moving pieces, and especially in this Flash heavy meta, it is crucial to be aware of when your opponent does not have their Flash up for Offensive and Defensive plays.
I think that showing the Cooldowns of Summoners will go a long way to facilitating a more aggressive game across all levels of play.