I don't have any special knowledge, but not sure why 8 is such a nonsense possibility. Switch came 3.5 years after the stationary consoles and had half the RAM. Next Switch coming only 2.5 years after the stationary consoles and still having half the RAM would be a slight improvement. Next Switch coming only 2.5 years after the stationary consoles and having 3/4 the RAM would be a huge improvement. If next Switch had gained RAM from its predecessor at the same rate as the stationary consoles, we might expect it to be around 7.2 GB (were such a thing possible).
I'm not ruling out 8GB, but they might be limited by availability of parts. From the Nvidia leak it seems very likely that Drake has a 128 bit LPDDR5 interface. That means they have three options for parts, either a single 128 bit module, 2x 64 modules, or 4x 32 bit modules.
A 128 bit module seems very unlikely, as they're very rare to the point of being almost non-existent. I believe Apple have used 128 bit LPDDR3/4 modules in the past for a couple of their iPads, but I don't know of any current devices using 128 bit LPDDR5 modules. If they do exist, they're likely to be much more expensive than using the much more common 64 bit modules, so don't really make much sense.
Four 32 bit modules are also unlikely. They're unlikely to ever be available in sizes smaller than 4GB, which makes 16GB the floor, and they will take up precious board space, which won't be easy to make room for if the new Switch is a similar size to the current models.
Two 64 bit modules seems most likely, as it means the same dual-module board layout as the current Switch, and 64 bit LPDDR5 modules are plentiful, and will likely continue to be for some time.
So that means they're either looking for a pair of either 4GB, 6GB, or in theory 8GB 64 bit LPDDR5 modules for the new Switch. On the top end (although I don't think it's particularly likely), they can easily get hold of 8GB modules. Flagship Android phones typically use 64 bit memory interfaces, and have used LPDDR5 for the past year or two, with 8GB being reasonably common. The 6GB 64 bit modules are less common, but do exist in at least a couple of phones, namely the Pixel 6a and, according to rumours, the iPhone 14 Pro (although we'll have to wait for a teardown for confirmation on that one).
A pair of 4GB 64 bit LPDDR5 modules may be a bit harder to come by. They may not ever be used in phones, as high-end models use larger capacities, and mid-range and low-end phones typically use 32 bit memory interfaces, so although Qualcomm's new
Snapdragon 6 Gen 1 (their first mid-range SoC with LPRRD5 support) has arrived, its 32 bit interface means the modules paired with it won't be much use to Nintendo.
The more likely use-cases for smaller capacity 64 bit modules would actually be laptops, as we're now starting to see LPDDR5 support in laptop SoCs, and as they typically use a 128 bit memory interface, a dual 64 bit module setup is common. I had a search for laptops using Intel's 12th gen "Alder Lake" processors, and although it's common to find higher-end models equipped with LPDDR5, they seem to start at 16GB of RAM, with lower-end 8GB models sticking with cheaper DDR4 memory. I didn't do an exhaustive search, though, so maybe there is an Alder Lake laptop model out there equipped with 8GB of LPDDR5, and therefore two 4GB modules.
I did actually manage to find one device shipping with 4GB 64 bit LPDDR5 modules, and that's
the M2 MacBook Air, which in it's 8GB configuration uses a pair of SK Hynix 4GB chips. However, the caveat here is that Apple embed the RAM within the M2's packaging, so they're not using standard off-the-shelf components. It's possible that SK Hynix could also offer this in a standard BGA package that Nintendo could use, but I'm not sure how custom they are (Apple claim lower latency for their RAM packaged on the M2, so there may be non-standard timings or other customisations involved).
Part of the issue as well is about how many suppliers there are, and how long the parts will be available. When a phone manufacturer is designing a new model, they only have to be concerned about parts availability for a year ahead, but for Nintendo they may still be manufacturing this new Switch until the end of the decade. This means they don't want to be in a situation where they can no longer obtain the parts they need, or be stuck with only a single supplier who charges extortionate amounts. RAM is particularly sensitive on this point, because they have very little flexibility to work around the parts no longer being available, without redesigning the SoC at potentially great expense. I suspect this is part of the reason they switched to LPDDR4X with Mariko, as long-term availability of LPDDR4 modules didn't look good, whereas LPDDR4X will still be around for a while longer.