YouTube link preview not showing up in WhatsApp
The best solution I could find was to adapt the URL copied in the share button

https://youtu.be/bDPczGUovzE

to

https://youtube.com/embed/bDPczGUovzE

This is basically substituting youtu.be with youtube.com/embed leaving the last part (in this video, bDPczGUovzE) untouched.
So now we can see already a preview before even sending

Once sending it we'll see


Edit
As of today this issue is already fixed and Beta users of WhatsApp can already take advantage of it.