I am afraid, that at this stage I won't be able to offer you a viable workaround of the discussed, that would allow you to use the two DataSources approach demonstrated on the How-to article.
What I could suggest you instead is to read all the data from the remote with a simple AJAX call, pass the data to the Scheduler DataSource as an array
and manually send the entire data from the Scheduler to the server, when the Save button is clicked. Keep in mind, that such approach would have some disadvantages compared to the option to communicate with the server using a Kendo DataSource. For example, the entire data should be transferred between the client and the server on each save. Also, you won't be able to use dedicated Create, Update and Delete endpoints for the different data actions.
As per the possible fix, I won't be able to offer you an estimate of when it will be available. This highly depends on the other tasks we have in our backlog. Therefore, I would recommend you to keep tracking the GitHub issue
for any updates.