I asked around in the Office Hours Discord and got a few responses.
In response to me outlining my suggestion to go for a powerful Windows computer, one person wrote:
I'm sure you are right, but I thought I would mention that if you can dodge the dreaded orange dot by not having anything access the microphone then a basic M2 Mac Studio can support 5 4k60 displays natively. The Studio Ultra support 8 displays natively.
"Four displays with 6K resolution at 60Hz over Thunderbolt and one display with 4K resolution at 60Hz over HDMI"
This doesn't reduce the points of failure though, just the cost.
Another wrote:
Not sure it helps but we regularly output 3-4 4K video outputs to a DeckLink 8K Pro via a Sonnet with QLab from an M1 Mini 16GB. These are at 25-30fps rather than 60 but is considerably cheaper than a Studio. So am sure Izzy could do the same or better.
A third wrote:
I really like the decklink with Isadora fyi
Best wishes,
Woland