The other important aspect of USB-C versus MagSafe is that I have USB-C cables hooked up on charges all around my apartment. There's a multi-port charger at my desk, one in the living room, and another in my bedroom. Laptop uses the same charging cable from these as my iPad does. Sometimes I hook another charger up in my kitchen if I'm using my iPad for recipes and want to charge it while I cook. There's another a USB-C charger that lives in my bag, along with a USB-C cable which can also charge my iPad and a power bank.
Even if they make this a new cable with USB-C on one end and NewMagSafe on the other, it'd mean buying a whole bunch of new cables if I wanted to actually use it. And I'd need to buy a whole bunch of chargers too, because the ones I have are mainly a single USB-C port and a couple USB-A ports.
If they want to make yet another proprietary charging cable, fine. I don't really care as long as USB-C charging is still supported.