I quite like it, and with the recent shift to working from home and decrease in travel over the next couple of years I think I'll stick with this set-up for the foreseeable future: powerful desktop driving 3 5k retina monitors + cheapest laptop or ipad I can get away with on the go.
Hence the Magsafe.
>touchscreen or keyboard attached
Hence the updates to the wireless keyboard, touchpad, and mouse.
>Seems extremely unlikely to do this instead of just getting a laptop or tablet given the price.
This is the wrong way to think about these features. Yes, if this is your only use case for the device you are better off with a laptop or tablet. If this is something you do occasionally, but you primary use case is for a desktop, the iMac can now serve both uses and save you from purchasing a second device.
Like when the family gathers around the computer to look at photos or FaceTime at Christmas.