It's probably worth noting that NVidia hasn't updated their portable Shield line since then because of their agreement with Nintendo not to release products that could be considered in competition to the Switch.
However, NVidia did say they expected the agreement with Nintendo to be long term, upto 2 decades, while Nintendo said they expect the Switch to have a significantly longer than usual lifecycle, as their handhelds lines often do. Nintendo often releases mid cycle processor upgrades (GBC, DSi, new3DS) even if they generally went unutilised in the age before OTA game updates, so I expect they'd want to maintain the Switch line for quite a while, and they'd realistically need a SoC that didn't break compatibility with the GPU in the current Switch with any upgrade. I can't see them wanting to go through the significant back end software work to enable all the current games, which utilise pretty hardware-specific low level APIs on the GPU side, to be able to be recompiled and likely rewritten in some parts of some implementations for AMD hardware.
Nintendo only used off-the-shelf hardware for the Switch because they had low investment capital, they needed to minimise risk and up front cost. I think it's more than likely they'd get NVidia to do a semi-custom part now there's guaranteed success, in theory they could probably get a big enough jump by just shrinking the X1 to 7nm EUV but then you can do a relatively simple drop-in for those ARM licensed cores with some more modern variants(A57 for A76 and A53 for A55 say) , the hard decisions would be with the GPU side of things.
