That's a nice question @Z!
It really depends on ExtJS release policy.
We just found out today the documentation available for ExtJS 6.2.0 at docs.sencha.com, and it was a surprise for us. There weren't either private nor public release packages for this version, so, we are really not sure how it is going to be out and why it skipped 6.1.0. Possibly a mistake by letting that API docs available to the open? We don't know either!
But as the component is imbued to ExtJS 6.2.0 it seems that, like the Pictos font pack we incorporated in Ext.NET, the license will be just the same. That is -- if 6.2.0 would really be released. If that was a mistake that could be possible that the calendar may be bumped to ExtJS 7.0.0, for example, which would mean a new major Ext.NET release as well -- thus a new license. This is, by the way, one of the ways the component would not be included to Ext.NET 4 -- again, if ever released.
So, if the component is released in 6.2.0 odds are in favor of being included with Ext.NET 4 license.
If the 6.2.0 release does not actually make it to be fully released in the commercial licensing terms of ExtJS -- or is released under another version or a separate plugin (like the pivot grid) -- then probably not to be included on Ext.NET 4.
Bottomline, not certain what's going to be 6.2.0, we'll have to wait and see!