Someone is working on replicating echo show functionality in home assistant, it's called View Assist.
homeassistant
Home Assistant is open source home automation that puts local control and privacy first. Powered by a worldwide community of tinkerers and DIY enthusiasts. Perfect to run on a Raspberry Pi or a local server. Available for free at home-assistant.io
Thanks, I like the look and implementation of that. My hub replacement may (or may not) have voice built in. Either way, this may be the way to go.
As conext: I've been planning to use the new on-device wake word tech with a few ESP32-S3-BOX-3 scheduled for delivery later this month. Since I posted the above, I've learned the planned ship date has moved to late May. (shrug) Now my local voice assistant plan is delayed.
The ESP32s would be my voice & presence detection devices (if they work as I expect). The hub replacement can almost be dumb, although I am picturing it running in a full-screen browser window - like found in what you linked and possibly using that very solution.
I'll add: ideally I'd like the slideshow to work while we're in the area, and for the screen to go dark after a set time and/or HA knows we're in bed. I can have a radar/sensor flag if we're in the room, so any hardware wouldn't need to have it.