You just showed a Vega 64.Of course. I thought you were talking about "tested" off-the-shelf configurations.
I would imagine that the Vega 64 isn't an option in the BlackMagic line due to power supply requirements.
An overclocked Vega 64 would have to be looked at. I would imagine that BlackMagic just wants to use a card made by AMD. And they are targeting professionals.
A simple enclosure without fancy stuff (USB, etc) should be fine if you stay within its limits.