Want a "Last Fight" Ending Game Mechanism

An idea just occurred to me, that a "no-turning-back fight" mechanism could bring magnificent change in game ending period, especially in a losing game. Mainly my theory is to give the losing side a chance to have invulnerable ability (either on champions or on the base crystal) at a certain price.

For example, when the main crystal has HP below 1500, the team can decide to activate invulnerability on base crystal for 30 seconds, but after that the main crystal enters "exhausted mode" , that it cannot regenerate HP as usually for 300 seconds. Alternatively, players can choose to use the invulnerability on champions,like when the main crystal has 1500 HP or below, the whole team get shielded invulnerably in 5 seconds, within the region of high ground while their mobility can be violated (slow, root, or stun). After shielding, the crystal cannot regenerate HP for 5 minutes.

This act should be based on a team agreement, so we need a voting process. Players can change their ward slot to a special key could planted near the main crystal. If five ally keys are placed around the base, the invulnerable shield will be switched on.

I know this greatly change the game. However, this might give hope to an awkward losing end, for instance, thousands of minions and super-soldiers pull down everything after ace. Also the outplaying team will need more consideration if they plan to rush the fight. The last defense mechanism will emphasize team fight strategy when all 11 towers are already down.

Furthermore, this mechanism endues more meaning to the main crystal in the entire game. The crystal is the final goal, but it has too less interaction during the game. It is so harmless to enemy and provide no good to the owned team. At least it should be given a function in the game, not just getting destroyed.