No manufacturer, not even Mercedes Benz can ever compete with the heritage and long establish cult status of the factory built VW Campervan. So when an offering like this pops up, regardless of how good it is, it will always start off playing second fiddle. Many savvy buyers will naturally think about depreciation and discount it straight away on that basis alone. But along with that these alternatives are often not that much cheaper either.
Then there's the build quality. With the exception of the Marco Polo, nothing that I have ever seen has come even remotely close to that of the California. Last summer, whilst mooching around a large steam fair in Suffolk, I saw a brand new Ford Transit based Wellhouse conversion on a trade stand. The design, layout and overall look was reasonable but the fit and finnish was not even in the same league. There was stick on carpet, huge gaps, some rough edges and it lacked the all important feeling of engineered precision. From memory they wanted around £50k for it so it was cheaper but not by much.
It remains to be seen what this van will be like in the flesh, but I can't see current California owners being wooed away or great future sales figures either.