My guess...

WRC 2018:

M-Sport (probably not Ford backing):
-Elfyn Evans
-Teemu Suninen
-Tidemand/Camilli (DMACK-Maybe they will have with two cars)

Citroen Total Abu Dhabi WRT:
-Sebastien Ogier
-Kris Meeke
-Breen/Loeb/Qassimi (Maybe Lefebvre too)

Toyota GAZOO Racing:
-Jari-Matti Latvala
-Ott Tanak
-Esapekka Lappi

Hyundai Motorsport:
-Thierry Neuville
-Andres Mikkelsen
-Sordo/Paddon (Share third car-maybe have 4 for some events)

OneBet Adapta WRT (if team will have enough money):
-Mads Ostberg

WRC2:

Skoda Motorsport (if they stay in sport):
-Juso Nordgren
-Jan Kopecky

Hyundai HMI Italia:
-Jari Huttunen

PH-Sport (Citroen):
-Stephane Lefebvre (Maybe Breen too)

M-Sport:
-Kalle Rovanperra
-Eric Camilli

Proton, Opel & Volkswagen will probably not competing.