Here's a comparison between former and existing cars and what seems to be coming just to put things into perspective. The numbers are what I could find so if somone knows better I'm happy to be corrected.

WRC 2011-2016
1360 kg with driver and co-driver
global race engine (1.6T I4) with 33mm restrictor ~ 310hp
limited aero

WRC 2017-2021
1360 kg with driver and co-driver
same engine but with 36mm restrictor ~ 380hp
lots of aero

Rally1 2022-2024
1430 kg with driver and co-driver (hybrid system is 84kg)
same engine as before but with hybrid boost ~ 380hp + 136hp = 516hp when boosting
less aero than previous gen but still relatively complex

new Rally1 2026
weight unknown
engine unknown but with fixed torque curve and max power 330hp (basically everyone will have the same performance)
common safety cell, aero and center of gravity tightly controlled and capped, top speed capped (sounds like some form of BOP)
design and car shape more open than previous gen
Rally2 based transmission
400k cost cap

Some speculation about 2025:
Since they say that in 2026 the current Rally1s will still be allowed and their weight, aero and power will be reduced I assume that means they will adjust these cars to 330hp like the 2026 spec and equalise the weight or something close to that.

About the Rally2 kits:
Current Rally2
1390kg with driver and co-driver
engine with 32mm restrictor ~ 290 hp
limited aero

Rally2 WRC Kit 2025
engine with bigger restrictor
larger exhuast, optional paddle shift gearbox
rear wing

They say they want to bring them closer to Rally1 performance so assuming the target is 330hp is it possible to get there with just the larger restrictor and exhuast? On the aero side it depends how much they limit the Rally1 aero, not sure just a rear wing will be enough. Also these cars might need to lose weight which I'm not sure is possible. This WRC kit only really sense if they can get them really close to the new Rally1. I've seen people compare it to the 2011 era RRC however there is a key difference: that car was a more expensive car downgraded while here they are uplifting the performance of a cheaper car. It might work if they can achieve the performance level.

So for 2025 manufacturers need to downgrade their cars by removing the hybrid, lowering power and simplifying the aero and they can keep using them for 2026. That's quite some work on the aero side and retesting the engine but you can then use the car for 2 years at least. New manufacturers or tuners could come in 2026 using the new Rally1 rule.

In the end we have to see the full rules written down but I think the key change is the performance cap. That was in fact what attracted a lot of teams to WEC, according to interviews with manufacturer representatives that i've read. They had a sort of guarantee that if they can reach the performance target they will be competitive without getting involved in an expensive development war. Indeed for this season some of the teams have changed nothing on their cars. The biggest changes will be made by teams that are having issues with performance or reliability. Robert Reid was at the Spa WEC race last year and is now at the Qatar race so maybe they're getting inspiration from there.