The biggest features of the XOOPS Cube major version candidate are TCB-like Drvie Mechanism and Rendering Sequence. These implementations mean that the XOOPS Cube core layer will have Controller of MVC. In other words, XCube_Controller may become unnecessary existence. It's another solution that XCube_Root may delegate Drive Mechanism to XCube_Controller. But, in this case, sub-classes of XCube_Controller can override common Drive Mechanism of XOOPS Cube. For the keystone of the major version candidate, that's bad idea.
BTW, the TCB-like Drive Mechanism of the major version candidate doesn't rest on the web technology. So we may have to stop describing it as MVC to prevent misunderstanding, even if XOOPS Cube's way is a kind of MVC.
(I don't know the details of the web technology, so I don't know that the web technology may have such the mechanism. Anyway, I took this technic from common computer programing technics.)