Exactly. And if there is demand for a London-centric HN, there is an even bigger demand for non-Anglo alternatives. There are huge markets outside of the Anglosphere.
I'd love to have a local HN to see what's going on in my country's scene.
I think HN clones like this should always be encouraged.
An example -- HN clone in Chinese language: http://news.dbanotes.net/
HN community, culture and politics (and also its moderation) are very Silicon Valley / US centric. This comes through especially on non-technical (but relevant) topics, like regulation. But also topics like company culture are extremely US-centric.
Localized topics (both in terms of content and culture) is probably the only reason why an HN-like site would be viable.
From my perspective it's definitely desirable, and just the current frontpage of technews.london confirms that there is a lot of stuff that will never make it to SV-centric HN.