I thought about that recently while researching how VCRs work before attempting to fix one. I didn't even think about seeing the actual video signal, I was just curious what the diagonal lines and control pulses on the tape look like. There are many other things as well that would be interesting to look at (all kinds of tapes, all kinds of floppies, hard drive platters, magstripe cards), but unfortunately I don't think there exists a technology capable of visualizing magnetic fields with enough precision.

I have a magneto optic sensor that can visualise the field lines of a magstripe when using a polarising microscope - https://www.youtube.com/watch?v=c8nM4Z-hkTw

I'm going to try a VHS under it, to see what I get.

Please do share if this succeeded :)

Thoughts on that: (1) you'd need a way to visualize the magnetic fields, (2) the data is frequency modulated, (3) due to helical scan, the video field lines do not line up evenly one over the next as they did so nicely in the Laserdisc / CED (there'd be a skew).

So I don't want to say it's impossible, but I think it would require a lot more creativity.