I Haven’t got the faintest idea what this is.
Edit: could this be about porting the Switch OS to a new SOC?
In the context of a consumer devices, FPGAs would be mainly used to prototype new integrate circuits. Companies like Nvidia, AMD, Intel, etc, use them as an important step in validating new designs, but they're also useful when designing any kind of integrated circuit, big or small. Nintendo obviously don't design their own SoC, but their hardware often includes a lot of custom ICs, and there's nothing stopping them designing their own chips in-house if they have a very specific need that wouldn't be covered by off-the-shelf hardware. They could also be doing pre-silicon integration testing for a part that another company is designing for them.
As to what they're specifically building in this case, I can offer some speculation. The posting specifically mentions
Gstreamer in the duties, which is a multimedia framework. They also mention
V4L2, which is collection of video capture drivers for Linux, and media-ctl, which is part of V4L and is also, unsurprisingly, related to media on Linux. Therefore, it seems likely that they're prototyping a chip which handles audio or video capture, streaming or playback in some form or another.
A standalone codec chip is unlikely, as that would be covered by Nvidia's codec hardware on the SoC. Any kind of standard camera, display or audio device could also be ruled out, as they're all handled by easily available* standard ICs. I would hazard a guess that wireless video/audio streaming of some kind is possible. Nintendo obviously did this before with Wii U (using Broadcom hardware, I believe), and it's exactly the sort of use-case where they may want a custom IC to minimise latency. Streaming from a handheld to a TV, or vice-versa, is definitely plausible, although they've already done that with Wii U, and the Switch approach of simply docking the "handheld" has clearly been more successful for them.
My slightly out-there prediction is that it's for streaming to some kind of AR headset. I saw people were recently discussing the use of a new Switch model to slot into a VR headset (a "proper" version of Labo VR, so to speak), but I don't think that's very likely. Firstly because the headset would be very front-heavy and uncomfortable for anything other than short play sessions, but also because I don't think the closed off format of VR is something Nintendo is particularly interested in (which they've stated in multiple interviews). Local multiplayer is still an important feature for Nintendo, and more than that, Koizumi stated that during development of the Switch
being able to play games while facing each other was something they wanted to achieve:
Ever since the first prototype back in the early days of development, I would ask Kawamoto: “Couldn’t we make a game where players look each other in the face?” That idea eventually gave birth to 1-2-Switch, but this wasn’t a concept we came up with out of the blue. It was something we had wanted to do for a very long time. We would often wonder why it was that you could play card games face to face with your opponents, but not video games. Our company originally made karuta and playing cards, so it has been a very influential concept for us since the early days.
VR is pretty much the opposite of this, but local AR multiplayer would fit directly into this vision. Being able to share an augmented reality space would allow people to play video games while facing each other, not just the TV, and I could see Nintendo's game designers having a lot of fun with it. Nintendo have been playing with AR for a while, from the built-in 3DS games to Mario Kart Home Circuit on Switch just over a year ago. They also have experience with low-latency video streaming, and taking a wireless streaming approach to AR (as opposed to other AR headsets, which I believe pretty much all have in-headset processing) would allow for both lower cost for the headset, and better graphical hardware behind it.
Of course even with wireless streaming sorted, Nintendo would have to fix a lot of issues with current AR hardware. Price being the obvious and most important one, but also limited field of view being another. There's also the issue that, if you want to use them for local multiplayer, you'll need multiple headsets (price again), and would a single console be able to stream to multiple headsets, or does everyone need both a console and a headset?
I could see it being a part of Nintendo's post-Switch plans in 2025 or 2026 or so. There seems to be a lot of money going into developing consumer AR hardware at the moment, so Nintendo may be able to leverage some of that research and reduced component costs. They could release a device which can still play in handheld and/or TV modes, but also supports wireless AR headsets. Keep BC with Switch, but make it very much its own thing with the AR support.
*Well, aside from the general chip shortage, but designing your own display driver IC isn't going to help you with that.