I remember making something with the LM1881 chip used here to remove copy protection from analogue composite video signals. Needed so VHS videos you bought played properly on my TV! Some things never change...
Well, yes, a crt oscilloscope in X-Y mode is just a crt monochrome television without sync generation and a fixed brightness. Back in the early days many people used to make their own oscilloscopes from 'cheap' TV tubes (only downside usually being that a TV tube had less phosphor than an oscilloscope really needed).
Scopes made out of modified TV boxes are slower because TV CRTs use magnetic deflection (through those big coils on its back) which is slower compared to electrostatic deflection used in "real" scopes CRTs. That is, even adding high quality input circuitry, the frequencies used and TV CRTs nature won't allow much beyond audio frequencies. That shouldn't discourage experimenters though, as even a 5 bucks ex flea market portable b/w CRT mini TV could still make for example a really nifty curve tracer once paired to a cheap MCU generating the necessary signals.
Does a TV tube's use of magnetic scanning not present a considerable difficulty in using them in an oscilloscope? IIRC, a CRT television typically used some rather hackish special-purpose circuitry to linearize its horizontal and vertical scanning, each just at one specific frequency?
The build I have seen was driving the electromagnetic steering coils directly, bypassing any original TV circuitry.
I imagine so, but you still have to deal with the underlying problem -- the coils are an inductive load -- and not just at one scan rate, but over all the scan rates you are using and at all frequencies in the signals you are displaying.