PCB layout for 8-16MHz crystal very near WiFi module AND small DC motor
Your general crystal layout looks pretty good. I've seen plenty of examples that were 10 to a 100 times worse than what you show here! 

Have you considered the possibility of using an MCU that has its own onboard oscillator thus eliminating the need for concerns about an external crystal?

Is there any possibility that you can share some other frequency source to drive the MCU such that the source generator is away from the motor and WiFi module?

What is the dead ended trace as highlighted here in yellow area? Is that an intentional trace to shield the two adjacent traces from each other? If it is GND shield trace would it be in need of a via a several spots to tie it into the GND plane?