They're using NDI to gather thumbnails if I remember correctly. NOT the smartest way of doing things and eats up a ton of processing just for the noobnail's
TBH I've never seen anyone use the streamdeck for punting, I've seen a TON of people use it to trigger scenes which includes clips (among 10 other things) but for punting, why? You already have the thumbnails on your computer.
With the webserver you should be able to pull thumbnails from the system and then apply them to the streamdeck but I think you would have to scale the thumbnails first (72x72 px, right), so maybe the functionality isn't there yet natively (getting some middleware to make the scale would probably be needed.)
But at that point, why not just use the webserver on a tablet to do what you need? (You can even send out a OSC command from connected clips to fire off other streamdeck events via companions OSC-In function.
I 100% get what you're after and yeah, steamdecks are great hardware and tbh, companion has been the biggest revolutionary software for our industry in a decade (IMO) but the juice isn't worth the squeeze IMO, especially when there are several different ways to achieve the same result. In the end, who "needs" the thumbnails? I mainly build out elaborate streamdeck builds for show directors on massively large shows, and they don't want thumbnails, and if you're working a music event (much different than these shows that have directors) you're already punting with the machine in front of you with thumbnails present (I use streamdecks on these events to, but mainly for FX and mappings). I can think of 50 other requests I rather the dev's spend their time on right now vs this. (My perspective is what should the dev's be focusing on. Stuff that doesn't have a workaround).
so sure, a +1 for me in a few years when all the bugs and major feature requests are built out first, (Like multi channel audio, global presets, 3D support, etc.
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Not trying to shit on your idea (I'm for it, eventually), just giving a bit of a different perspective <3