This really is about Keybase bringing expertise with identity to the table and it makes a lot of sense for the two teams to work together. The currency side of things is still going to be handled by Stellar as far as I can tell.
Here's how normal people look at something like this. It's not "oh, but they're just facilitating," it's "why is there cryptocoin crap in this thing we use for work?". Then it's "Ed, why is this thing you recommended and spoke so highly about doing this? Are they cryptomining on our computers now?". Then, even after an explanation, they're probably still suspicious and probably right to still be suspicious because the cryptocurrency universe is, by normal and sane people, still viewed as a scammer's paradise. (To be clear: is this entirely justified? No, and I think there are decent people trying to make a go of it. But there's plenty of dirt going on and people should be suspicious until it's proven otherwise.)
I don't want this on my computers. But, more than that, I don't want my clients thinking that I am a party to shady business because of the tools I recommend that they use.
There are obviously annoying ways in which keybase could support cryptocurrency, but you are making a lot of assumptions about what Keybase is going to do that are not based on the blog post. For example, wallets do not mine coins and Stellar does not support mining.
Why don't you wait to see what comes out and submit a feature request if you don't like it, instead of flipping out about some hypothetical feature you won't like.