There is no "later possible crash". In Pre-Init(), we make sure that only color space(s) are allowed that are actually supported, ie. YV12 here. You either convert in the renderer, right before output (not yet implemented in the DXVA2/-HD renderer), or you do it before processing if you have to (this PR).

As for your proposed change, no, it will be a major performance hit for people with low-performance GPUs (during fallback to PS rendering) or low-performance CPUs (during fallback to SW rendering), effectively disabling fluent Hi10P playback for them.

Performance was the whole point why I have been using this patch for almost 2 years now: I have an Intel G45 and using PS scalers for 10bit is a much worse performance impact than converting to 8-bit and using DXVA scalers, especially when actual scaling is involved (e.g. 720p->1080p). Color space conversion and subsequent DXVA scaling gives fluent playback, always, PS scaling does not.
That's why I said we should never, ever, fallback to non-DXVA rendering when a user actively chooses DXVA in the GUI settings.