Looking at what's been taken out of the past two MBP's (Ethernet/FW800/OD from rMBP and USB-A/mDP/HDMI from today's MBP), they've been the limiting factor for thickness of the lower body. So looking at what's left, my prediction is no 3.5mm jack in 2020. Taking it one step further, and dare I say it, no ports and wireless power in 2024?