Surely, this has been tried many times - Microsoft with XAML for WPF, Silverlight (Flash killer), Forms, Adobe Flex (MXML), Google XML for Android, XUL etc. etc. All seem to suffer from the problems that Visual Basic did not have and becomes obvious when you go beyond some simple forms. OP seems to a long timer in this space so surprising shrug
* difficulty in mapping complex UI layouts to XML (VB was quite literally WYSIWYG and mind-blowing for its time)
* Verbose to specify (esp. multilevel nesting, complex navigation etc..)
* Cannot make sense of the XML content vs all the nested tags
* Keep switching between how the UI looks and the XML
... all generally point to the difficulty of separation of configuration and behavior.
* difficulty in mapping complex UI layouts to XML (VB was quite literally WYSIWYG and mind-blowing for its time)
* Verbose to specify (esp. multilevel nesting, complex navigation etc..)
* Cannot make sense of the XML content vs all the nested tags
* Keep switching between how the UI looks and the XML
... all generally point to the difficulty of separation of configuration and behavior.