d future or plans for d3

[Robert Jacques]

On Sun, 18 Dec 2011 15:29:23 -0800, Andrei Alexandrescu <SeeWebsiteForEmail at erdani.org> wrote:
> Unions will be conservative. The golden standard is that SafeD can't use
> them or anything that forces conservative approaches.
>
>
> Andrei

Is there a strong rational for a conservative approach to unions? Why not simply set the GC pointer flag bit every time a union is assigned to? Given that there are fully precise GC implementations for C, why should D aim for something less?