Nowhere has London's tourism budget, so I doubt it would be as big, if even viable.
I don't know if it needs London's tourism budget; sportives elsewhere have been successful and viable too. Although like the LondonEssex they might suffer a drop in interest over time, hence my suggestion of moving it from year to year to keep it fresh.
The size of a future event would be down to ambition, how it's marketed, and the level of support from local or even national government. Plus flogging the nearly-dead horse that is the 2012 legacy, the right celebrity (shudder) endorsement, charity involvement, and linking with international events; eg the TdF (2007?).
Not sure why you're so pessimistic; I'd hope you'd be a cycling proponent.
Before covid, there was a sportive linked to the ToB. I know people who rode it but it seems you've not heard of it! The ToB uses rolling road closures for most of the route so the sportive wasn't on closed roads except the start/finish zone.
Nope, not aware. I rode out to spectate ToB stages as a spectator in the decade before the pandemic, but I wasn't aware of any associated sportives; I wasn't into road cycling at the time - but it was events like ToB that ultimately got me back onto road bikes after a long absence.
IT could work for others; the organisers could work the "active travel" angle and seek some funding from Keir.
The London stages of ToB tended to be circuits of fully-closed roads so not a great sportive opportunity but I did get to ride the closed course for an hour before the ride once, invited by BC. 2013 maybe.
The opportunity is there to fully-close roads when necessary (as with some large sportives). As you say, the race stages can usually get away with rolling closures; that's all about managing and reducing negative impacts.
Anyway, you're putting up barriers again ; The RideLondon organisers weren't so defeatist ; they took the existing Brompton World Championship, added the pro Classic and Classique races, the main 100 sportive plus two shorter routes. And added a scattering of other sportives (the 100 plus up to two shorter routes) plus the freecycle, BMX and youth events.
Pretty sure Danny MacAskill was invovled one year, and I certainly remember seeing a whole load of stunt riders doing his style of jumps and hops over various obstacles and a bus in a the middle of Kingston-upon-Thames marketplace.
It was a proper cycling festival - see what can be done with a bit of ambition and enthusiasm?