We all know that tunneling is a big problem with the game. Optimal play means that going after one survivor until they die is the best way to reduce gen repair speeds. Solution? Modifiers:

Basically I propose the addition of a buff called Urgency and a debuff called Crippled

Urgency: Every time a survivor is hooked or reaches a new hook stage besides you, gain a 5% boost to gen repair, healing, chest opening, gate opening and hook sabotage speed. This gives an additional 5% bonus for every dead survivor. This buff stacks with itself and is lost when you are hooked.

Crippled: Every time you are hooked gain a 20% debuff to gen repair, healing, chest opening, gate opening and hook sabotage speed. This debuff stacks with itself and lasts for the rest of the trial.

How does this help? So let 100% represent the speed at which a single survivor preforms gen repairs. At the start of the game survivors repair generators at 400% speed. Once a survivor is being chased it goes down to 300%.

With this change once the survivor is hooked the gen repair speed is 315% and will be at 395% if the survivor is saved. If he is hooked a 2nd time the gen repair speed will be 330% and after a 3rd time it will be 390% due to Urgency getting stronger. That's only 10% slower than the start of the game.

If you instead hook a different player the 2nd time then again there is another +15% gen repair speed. However once they are unhooked it is a -10% from compared to before they were hooked. 20% from crippling them and 5% from removing urgency. Each hook on a new person is worth 5% more than the last so your 4th hook on a new person will reduce gen speed by a full 20%

This also means that if you are better than your other survivors at evading the Killer than you get rewarded for your effort with extra action speed.

So if you evade the Killer the whole game while the rest of your team is killed then you will gain 9 stacks of Urgency for a 180% bonus to action speed (a total of 280% if you manage to never get hooked). Combining this with left behind means completing the generators yourself is a completely viable task.

At the same time if the Killer spreads out hooks instead of tunneling the game would be slower than it is now. Since after the first hook gets saved you've already slowed the survivor's down by 5%. And the next hook slows them down even more if it is on a different person.

Now of course while this system is great for discouraging tunneling it has an obvious problem. Specifically the time between hooking a survivor and finding the next one being a time where the Survivors are faster compared to if you never hooked them (315% vs 300%). Late game this isn't that big of a deal since the Killer would have momentum and thus would be able to gain the upper hand anyway. However early game this could lead to a quick genrush even sooner than it does now. This is great for dealing with campers, but not for people playing normally.

Thus we need something to act as a consistent buffer. Thus I propose as a secondary objective:

Parts!

There are 6 parts scattered across the map plus 2 in the basement. Each survivor can carry one part at a time and can carry one at the same time as an item. Before you can work on a generator you must find a part (which would be silver and somewhat shiny) and bring it to a generator. Once installed (which doesn't take long) you can work on the generator like normal. You must do this for each generator you want to complete once per trial per generator. You may use a brand new part addon in place of a regular part in addition to it's current effect. If you are hooked with a part then you lose the part and must find it again. If it was in the basement it is placed back there, otherwise it is randomly rehidden on the map.

This gives a larger incentive to traversing the map, especially early on. And it gives the Killer a stopgap before the generators start popping. It also makes the basement a more important location for everyone.

The Killer cannot see part aura's.

The details of this system are unimportant compared to the core idea of "Find a thing, bring it back to the gen, THEN start working on the gen". So don't get hung up on the specifics of what I just proposed.