Currently, if you attempt to type, paste, or select sample text containing missing glyphs in the Edit View, said glyphs will simply fail to be inserted.
I suggest that instead of these missing glyphs being blocked outright (or even automatically generated), blank transient glyphs should be inserted in their place. Making an edit to a transient glyph would go ahead and promote it to a real one; otherwise, no glyph would actually be generated. If you wish there could also be some shortcut to generate a real glyph for every selected transient one.
I think that just typing in the Edit View would be a fun and elegant way to discover and generate new glyphs 
. The transient glyph would also solve the issue of holes in pasted or sample text without the risk of generating unwanted glyphs. Although this request is similar to this one, I believe it is different enough to warrant its own topic (let me know if I’m mistaken).