More bans?

When will Riot add atleast one or 2 more bans for each team to balance out the sheer number of "questionable" champs.

Probably never.

I'm not sure Riot really wants to highlight the covering-their-mistakes aspect of banning (which usually only applies to a guy they just released or re-worked in the first place, which 6 covers).

They might expand it for reasons related to other uses of bans though - like forcing that game-changing player onto a different champion, allowing champions capable of countering strategies to be removed from the table, and simply banning out champions you don't want to play against for whatever reason.

That said - champions in LoL are very rarely broken. They're set up on a pretty respectable gradated curve of power that goes from about 55% win rates to 45% win rates. It would certainly be nice if everyone just had a 50% win rate, but as LoL's balance usually stands - if you ban out the top 6 champions, there will always be 6 more top champions that are 1% stronger than everyone else due to removing the 1% stronger than them. Ban out 15, 30, 45, 100 champions - same basic deal. As balancing them all to be exactly as powerful as one-another is likely impossible you're mostly just making picks/bans take longer by adding more bans to deal with the "questionable" champions.

Another con of more bans is the fairly limited champion pools of the average LoL player as well. More bans means a greater likelihood you're preventing the average player from being able to switch to alternate lanes and take up different lanning positions. It also increases the capacity for a team to entirely ban out a specific lane, as well as arbitrarily banning out a specific player.

Anyways, if the only thing players are going to use bans for is to hit the top 6 "questionable" champions Riot doesn't have any real incentive to expand the number.