There are several new features that are going to be released this year like Custom Functions or Dynamic Arrays which are extremely critical for our Addin and our customers. And those won't be available for retail version of Office 2016/2019
Microsoft should provide at least one time update for the Office 2019 to support these features so our customers can leverage the functionality ASAP without having to wait for next retail version!
For us it is critical thing as there are quite a lot customers preferring retail versions over Office365 subscription.
There is no current plan to backport the functionality at this point.
I was a bit disappointed that after purchasing Excel for Mac I discovered that I could not create XLLs in a similar way as on Windows (besides a VBA workaround) and that the JS api is restricted to subscription only.
Florian K. commented
Same issue like Daniel T. Please also consider Office 2016 volume contracts.
Daniel T. commented
As we need this for one Excel Add-In we use within our company to access data from a BI platform and thereby support the self-service approach for business users, I like to stress the importance of the request. Please make latest Javasript API versions also available for the retail Office versions!