I am afraid we don't have plans to support such functionality in the future. RadAjaxPanel internally uses asp:UpdatePanels, which render either <div> or <span>.
Theoretically, if RadAjaxPanel renders a <tbody>, it will not be of much use, because you can have only one <tbody>, so you will be updating the whole table again. And the AjaxPanel cannot be rendered as a <tr> because you will have duplicate <tr>s - one from the AjaxPanel and one from the asp:Table. In short, I don't think update panels will ever be able to "inject" themselves and be part of some other element (control) HTML output.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.