I'd argue the iMac was a different situation because there was an immediate upside to using USB peripherals, namely they were much cheaper than Mac proprietary stuff. For example HP had a popular inkjet printer, the PC (parallel port) version was $150, while the Mac (serial port) version was $300. The floppy wasn't a huge loss either as most Mac users were using Zip disks.
There's no real advantage right now in using TB3/USB-C, because pretty much nothing else uses it. And I'd bet that, in 2020, USB-A, HDMI, DP, and even VGA will still be in common use, so I'll probably be using dongles forever.
I'm not sure that this time it will work out for them, that's not what I'm saying at all. Personally, I think HDMI is useful still. And I'm hugely sad to see the MagSafe go. I guess all I'm saying is it's not totally uncharted territory, or even that uncharacteristic of Apple.