I think it depends on the distance between the track and spectators, at Belle Vue and Stoke where there was a greyhound track in between, the 6ft catch fence wasn't required.
It's been over 23 years now, the last season in 1997 they won the league and the crowds were poor then, I cant see there being an appetite now. Maybe for one off bigger meetings.
I'm not sure where you have got that about initial costs, Belle Vue were using an external company who are being paid.
I didn't see the Edinburgh and Plymouth streams but I would guess they didn't have a setup like this with multiple people working those computers, plus at least 5 cameras with 4 camera operators etc, not cheap.
Why is all the discussion about tv deals. From what I understand this announcement was that Eurosport EVENTS have taking over the running and promoting of SGP/SoN etc from BSI in 2022. I presume Eurosport will take over the tv deal aswell eventually but that is secondary and the big debate should be how Eurosport Events will promote these series in future.