If there are, serial numbers wouldn't really say jack shit about it. They aren't even a good indication of a Wii being a boot2v4 Wii. It is possible to have an LU64+ Wii that isn't a boot2v4 Wii and it is possible to have one that is lower than LU64 that IS a boot2v4 Wii.
So in short, don't use serial numbers to judge anything. If you are buying any new Wii right now, it is highly unlikely to be anything less than a boot2v4 Wii.
I'm not sure if there are any Wii's in the US that can't read backup discs, nor am I even sure if they exist at all. If they do, I believe the rumor is that they are just the new black Wii's in Japan that are like that.
Even with those rumored drives, I don't think the systems themselves are "unmoddable", I think you can still mod them in the same way and at least get usb loading working on them.
So basically, if you're buying a Wii now, just follow a current guide like the ones in the stickies/my sig that DON'T involve downgrading ANYTHING other than IOS15 with the Trucha Bug Restorer and see how it goes from there.