Yea, I agree. Quins get 80,000 at Twickenham as they sell out every league match and it is very local to their support base. They also promoted it very well. Also, it's at Xmas when families are together and a good day out.
RL in London as a one off game will only be valid if they made the WCC there and gave themselves a few months of promotion.
I can't see 80,000 people showing up in London to watch Wigan v St Helens etc.
I admire their ambition... but a regular SL match won't set London alight.