BlackBerry 10.3.3 is now available for unlocked BlackBerry devices and some carriers are pushing it. More will as we get into 2017.
As you were informed, Let’s Encrypt certificates are recognized by BlackBerry 10 beginning with 10.3.3. Here’s proof:
This website was previously inaccessible on BB10 without a manual certificate import because the cert was not trusted. Now it is accessible and the cert is trusted. Yay!