All updates have their effects and they are being discussed here to arrive in the game correctly. If players want to persist in an alliance, no problem, the difference is that no one will depend on an alliance anymore.
What I think about gates.
When war is going on, map owners need to get to the GREEN gates to collect the medals. Because with the proposed update you won't be able to collect medals from a RED gate. Since you can't teleport from a RED gate when you have dueliest during war, you can use the shortcut gates to cut across the map and reach green gates.
(Big advantage to defender)
1v1 situation.
Attackers and defender have more escaping option using shortcut gates
(advantage to both)
-Group fight situation when more defender than attacker.
Attackers will be chased down faster.
(advantage to defender)
-Group fight situation when more attacker than defender.
Defenders will be chased down faster.
(advantage to attacker)
Important: Honestly though in what server do you see more attackers than defenders?
What I think about alliance.
Alliance will still persist because I know that for players who just want "fun" it is TOO easy for them to just stay in an alliance and wait for sheriff. I can only see people who are already sheriff leaving their alliance, I really can't figure out why a non-sheriff would leave their alliance. ( Most players are lazy, weak and when they see 1v2 they will start to cry. I can't imagine those type of players leaving their alliance).
If there is someone brave enough to leave their alliance they will be targeted by all of the alliance which makes a 1v50 or 1v100. They would just be forced to join the opposing alliance.