The MPX filter and low response of ALL cassette tape in 1967 would also blow the theory away.
I don't doubt they may have tried...three companies were working on Laser read video, 1-2 on videotape (Cartrivision and U-Matic) and the science behind Selectavision CED was being developed. I'm QUITE certain such things were in development.
In BRITAIN.
BPI was anti-piracy long before any American concerns. Their share is tiny, it had to be.