I'm not so interested in a Retina display. I think the current 1440x900 resolution is great. Although it's not as detailed as the 2560x1600 display on the 13" MacBook Pro, it offers more screen real estate than the Retina display in "best for Retina mode" (ie simulating a 1280x800 screen).
Additionally, a Retina display will have higher graphical and power requirements to run it. I'm not sure the quality gained by those extra pixels are worth all that. If they change the TN panel to an IPS panel and keep the resolution the same, that would be a great improvement in my eye.
I'd also like them to keep scissor-switch keys and MagSafe. I'm neutral on replacing all the USB-A and HDMI ports with USB-C. It'd be nice to keep one old USB-A, though. It'd be kind of nice to keep that SD card slot, but not a big deal.
And this is mostly wishful thinking, but I'd really like LP-DDR4 SDRAM, ≤10 nm CPU, and this is probably impossible (overly expensive and overly-high thermal requirements) but on-package graphics (like Hades Canyon or similar).