1 - This would kill the purpose of PvP guilds that run premades, if the enemy team can just surrender early, the guilds will lose all incentive to queue for battlegrounds again since the enemy team knows the chance of losing against premades is high.
2 - In many battlegrounds, even when it looks like the enemy is losing, they can still make a comeback. For example, today in Warsong Gulch, we had capped 2 out of 3 flags, but one healer joined their team, and they managed to turn it around and win with 3 flags.
3 - In large battlegrounds like Alterac Valley or Isle of Conquest, teams would just vote to surrender, which is equal to removing them from the game (The suggestion of removing AV/IOC got denied many times )
Killing premades would be a major net positive, in my personal opinion, but that would be minor when compared to how people would abuse this.
If you are in a Battleground you consider "hopeless," leave and take the debuff. Even if this suggestion was implemented, you weren't under the illusion that it wouldn't give you Deserter the same, right?