I like the touchpad on my X1 Carbon, but I never used a mac long enough to really adapt my workflow to all the touchpad gestures (I think on Linux you'll be happy with general usage/scrolling/etc, but stuff like pinch to zoom is still not widely supported).
Surprisingly, some Tk applications that I use irregularly actually work with HiDPI with Tk 8.6 (as in, they are scaled up with an integer scaling factor, and are sharp).
Multiple displays with different DPIs also work with Wayland (I have one 4k screen and a LoDPI display 90 degrees rotated). Though, there are some bugs with GNOME 2.26 on Wayland with HiDPI displays that are switched off and on again (e.g. some applications such as GNOME Terminal become blurry, they seem to be rendered at lower DPI and scaled up). I have reported some bugs and the gnome-shell/mutter developers are quite responsive.