Don't Wait for a 17-inch 2018 MacBook Pro
The 17-inch MacBook Pro was a powerhouse of power and it offered a huge screen to work on, but Apple hasn't sold a 17-inch laptop for many years and it's unlikely we will see one come out this year.
Instead of waiting for a 2018 MacBook Pro 17-inch model, you should consider buying a 15-inch MacBook Pro and using the iPad Pro as an external display when mobile. This is still very portable and it works very well with an app like Duet.
Another strike against this idea is the fact that Apple supports external GPUs with macOS High Sierra, so if you need more power while still staying mobile most of the time, you can buy an external GPU to get more graphics power.