We have this feature in our plans and we will make sure that we will implement is as soon as possible. However, I cannot promise you that this feature will be part of the official release. In the meantime you can take a look at our new Software Development Kit
(SDK) that features how to build custom widgets and register them in Sitefinity's toolbox. We have a few step by step tutorials on how to build a widget from scratch.
We have plans to release official Sitefinity 4.0 by the end of the year. We will also have a release candidate about a month before the official version, however I cannot give you an exact timeframe for now.
Let me know if you have any other questions.
the Telerik team
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