Qt or wxWidgets, make a supported C iface (I am aware of some work on both fronts, e.g. wxc that was used by wxHaskell I think?). IUP and libui, thicken your libs (libui guy just got permission from his new company to get back working on the lib, yay). World, don't hate non-native-OS-widgeted apps. Browser vendors, stop being so tunnel-visioned into your my-OS-only, non-embeddable, or must-be-multiprocess shit. And let us trim some fat off at compile time please (waiting on you Servo, but please stay lean and single-process for embeddability). JVM AOT...we're waiting, we know it's coming.
And no, I would rather not have an interpreted (or dynamic) language if I can help it.
Edit: To clarify before a ton of responses pick apart my specific criticisms, I'm making these points to show there is a void. I could poke a ton more holes in these libs and more (I have used most), but it's hardly worth arguing the nuances here.