I found the answer here:
https://api4.windy.com/

"Windy API is not compatible with higher versions of Leaflet and we have no intention to upgrade so far."

Have you taken a decision against upgrading to 1.x or is it just a matter of funding/time/priorities?

"Would you like to develop your own Windy plugin and extend Windy's functionality?"

Yes!

Hi, I remember seeing a notice that the plugin only support NPM Leaflet 0.7.7 and that there are no plans to support 1.x at this stage? I can find the post now.

Can you confirm if you will support 1.x in the near future?