I think that it should be a combination of what we have now and being blocked from playing game modes.
A player with 3 3 minute LPQ timers not only has to sit through the timer, but is also blocked from playing ranked modes.
Playing brawl modes does not count towards taking you out of LPQ in this system, only by playing full 3v3 or 5v5 casual matches count. If you play brawl modes you will have to sit through the LPQ timer everytime until the conditions of release are met.
This coupled with being unable to log out like we cutrently have for LPQ players should probably ne enough to deter most players from trolling.
On top of all of this I would also like seeing full bans on players, on a scale for repeat offenders.
So the full system would look like this:
All players will be warned once before first offence status.
First offense: Locked from ranked with three 3 min LPQ timers.
Second offense: three 10 minute timers.
Third offense: 1 day ban from the game with 5 10 minute timers after 24 hours.
4th offense: 1 week ban from play, returning with five 15 minute timers.
5th offense: Permanently banned account.
All of this with a better detection system should be able to curb trolls rather quickly.
Offenses could be reset every month for each player with problem players being on a watch list to prevent abuse of the system. For example trolling just enough to get minor punishments and not trolling for the rest of the month to avoid more severe consequences.
Thats my idea anyways.