There is/was; the Muse Research Receptor. It might be overly complex for what you are thinking of, but it existed.
https://www.soundonsound.com/reviews/muse-research-receptor
https://www.soundonsound.com/reviews/muse-research-receptor-...
You can pick them up, often fully loaded with plugins, for a few hundred dollars. I wrote parts of the system. They were running Linux and fun to hack on.
I currently work in the professional audio industry and know of a few modern efforts underway to produce modern version of this, but I am not convinced there is market for such a device anymore.
That's a really cool. It doesn't look overly-complicated, just perfect actually. I might keep my eyes peeled for one of these things, I love scrounging around for old MIDI gear. Used to be a lot cheaper than it is these days, ironically. Build quality on most everything was top notch too.
I'm sure a lot of professional musicians would probably prefer to use something less fragile than a laptop, something you can rack up, with no pesky desktop OS niggles to worry about during a show. As you know many instruments today are simply dedicated VST runners with a handy physical interface, see Roland's Boutique and Aira synths. I have an MPC One which I love, it can run proprietary VSTs. Maybe such convergences have killed the need for a dedicated box.