Bug 366659

As all of you sure know, the mobile applications interfaces are "revolutionizing" the way users interact with computers, even if those computers are small portable ones. One of the interfaces I like a lot is Telegram's. In Telegram you don't need to leave the app to see online videos -at least from Youtube, haven't tried other sites-, it will show them within the app in a reduced size that fits your screen's width. Something similar happens with audio files: if someone sends you a song you can play it without leaving TG, it will play and show a tiny bar to pause/resume or stop the playing. I think Gmail has those functions too (I'm not sure of this for I don't use Gmail, I'm talking by hearsay)
Well, could this be implemented in Kmail? Of course computer's screen sizes are bigger than mobiles' and opening a dedicated app when clicking the file is not so annoying, but it'd be handier, the same way it's handier to see attached images inline and not need to open Gwenview or whatever similar program. Could this also be done for attached videos, not only online links? And the same for audio files: could a basic player be inserted in the mail view to play them?
And last: could this be done also for documents? Sure most people won't be eager to read long documents in Kmail, but would be rather handy to have a quick preview of PDF, Epub, ODT...

Reproducible: Always