I think on reflection I’m happy with the current setup. It does have the advantage of hiding my IP address from the server. I think it needs better documentation, and will write a how-to post [edited to add link] once I understand the other keysharing methods better (I started dafting one a while ago).
I can see the argument for integrating WKD into all mail clients; it is similar to the argument for Autocrypt. I don’t think DC should be an early adopter, tho; I want to retain the secret-public-keys system anyway, and the advantage of open standards is that we can wait and see how other mail clients handle whatever problems come up with WKD (Will encrypted spam become a problem, for instance? Will WKD give servers more metadata and users less privacy? Will there be MITM attacks, from the servers or DNS poisoning?).
Deltachat also has “You don’t need to trust the server” as a strong design principle, and if I get my keys from a hidden page at one unmirrored server (which is what happens, if I understand WKD correctly), then I really need to trust it! This could be especially problematic for users in authoritarian countries.