Wait for a New MacBook Pro Color
Apple sells the MacBook in four color options, but only offers two MacBook Pro color choices for the 2017 model. We could see Apple add in a third MacBook Pro color option this year now that they've had plenty of time to iron out any issues in the supply chain.
It's unlikely that Apple will dramatically change the 2018 MacBook Pro design, so adding a new color is one way they can spice up the looks of the model while keeping production running smoothly.
Rose Gold and Gold are popular color options on Apple products and if Apple only adds one, we'd put money on a Rose Gold MacBook Pro in 2018.
This isn't a huge reason to wait, but if you like to express yourself with the base color of the MacBook Pro or want it to match up with your other Apple gear it is a consideration.