Reducing mana availability will not make mages more interactive
One argument I read here was that PvE clearing minion waves was not fun and uninteractive, that's why we need mana changes.
Newsflash here for Riot: If you have less mana available, you will not suddenly decide to use your sparce resource to trade your lane opponent. That's how you end up out of mana, unable to get mid priority or even unable to farm because you can't do shit against the AD casters/assassins. You will be much better of just saving whatever you can and do the least needed. Rather than change mana this way, change the champions that are so strong at waveclearing (btw Lux on surrender at 20 gets changes for easier waveclear (E changes), why do that if there is too much waveclear).
Have a nice day all :)