It would certainly be nice, but I don't think DuoLingo's software supports the addition of furigana.

It is unlikely that this will be added to the course any time soon.

Yes it would be a very good feature for beginners.

Note that if Duolingo's Tinycards was to support HTML, we could just use <ruby> and <rt> tags. See also:

• https://developer.mozilla.org/en-US/docs/Web/HTML/Element/ruby
• https://developer.mozilla.org/en-US/docs/Web/HTML/Element/rt