This could be interesting, wonder if the demand is there for the added capacity new operators would bring, but judging by how much more expensive it is to travel midday vs morning/evening it does looks like there is.

Would be nice to have a proper budget option like what Ouigo is, not too bothered by extra destinations, if connections are better at the existing ones.

I registered when I saw this, just so I could share this really good analysis. It explains why expanding traffic through the tunnel (whether by Eurostar or competition) isn't as simple as we might both assume and hope.

https://jonworth.eu/the-future-of-long-distance-train-services-through-the-channel-tunnel/

A "rival operator" in the sense of route duplication seems utterly pointless. Assuming finite capacity and demand for tunnel crossings, that'll mean halving the customers for each operator carries, reducing opportunity for economies of scale, increasing complexity for ticketing etc. Unless there's some suggestion that Eurostar is price gouging (and they're hardly wildly profitable compared to other operators) it won't do much.

What we do need is more diverse routes with different destinations (so that not everything is a transfer at Paris or Brussels). There probably is capacity for that, but Eurostar (and other operators who have dipped their toes in) have generally concluded that the demand isn't there to make the routes sustainable (at any price).