I don't think that Web Components will grow much as-is, it's cool for relatively discrete UI components, but the lack of non-string property support and a good story for state management, I think React is generally better for most use, but you can combine the two.
I also do think that Web Assembly projects will mature, and should a better DOM story come to bear fruit that will be really nice. I have a feeling that access to Canvas and sound primitives will come ahead of general DOM access, which will have some really cool options for webifying more applications more easily.