Welcome to Product Dork @aharris!
I am kind of in the same boat. I’ve considered upgrading my MBP, but the thought of getting trapped in dongle hell and the touchbar have pushed me away.
From what I can tell there isn’t a definitive release date on a USB-C Unifying Receiver. All I can find are people bitching on Logitech’s community forums about it.
From those comments it looks like the current strategy is using a small dongle like this one to go from USB to USB-C.
I think it’s this dongle from Amazon. FWIW the Fakespot gives it a B, which is pretty good. CamelCamelCamel says prices fluctuate between $8 and $15.
Also, I’m going to change this topic category from Questions to General Discussion since I don’t think there is going to be a definitive answer here.