This part I cannot fathom. The era of 7-bit bytes is over. What can possibly justify the need for a "printable characters" encoding now? Something stupid like putting data in a JSON string? What's the next step, base-64 encode the JSON containing that string and put it in an XML tag?
<data><![CDATA[PD94bWw+PHdoeS8+PHRoaXNpc2F3ZnVsPjwvcm9vdD4=]]></data>
Bonus point if there's a situation where avoiding something like base64 is actually difficult, even in 2018.
For example, there is (was?) a bug in nw.js with using @font-face to specify a font url that is in the same (local) location as the manifest. As a hack I tried specifying the font as a base64-encoded data url. It worked!
I had no use for base64, other than that there exists an interface for specifying data and it takes a base64-encoded string.