Bikes on Eurostar?

That's the kind of dangerous extremism that gets you chucked out of the Labour Party these days.

Seriously, what you're suggesting requires political will (lacking on all sides currently) and coherent government transport policy, which would include taking the railways back into public ownership and raising the tax on aviation fuel/flights to an appropriate level. Not happening in my lifetime, unfortunately. We had a shot at that and we utterly blew it.

Completely agree on this but Eurostar would need government subsidy or nationalisation for this to happen, neither of which is likely under the Tories. And if Labour tried it I’m sure the nativist Tory right would be out claiming it’s only a benefit to metropolitan London elites, so I’m not sure it’s a vote-winner on its own. Would need to be part of a much wider package of public transport reform (which I think could be a vote-winner for Labour)

Why does it have to be about profit? Why not be clever and facilitate active travel and reduce need for cars? When the planet is underwater, your profits, as well as your Strava KOMs are gonna be fucked.

That Eurostar carries bikes at all is an anomaly in any case. From memory, but I can't find anything about it on-line, cycle carriage was only inserted into the legislation because of a Tory MP's (or maybe Lord's) intervention. I think the only other high-speed train, possibly worldwide (but I'm no expert on trains, so please correct me if that's wrong) to allow bikes on is the German ICE 4:

https://ecf.com/news-and-events/news/deutsche-bahn%E2%80%99s-new-ice-4-high-speed-trains-include-bicycle-spaces

When European high-speed trains first started in France in the late 70s, cycling was pretty much the 'forgotten mode', and at any rate the main strategy behind European high-speed trains has always been to facilitate business travel, e.g. the famous 'it's competitive with short-haul flights'. In France, this has led to a two-tier rail system, with very little investment into local and regional trains, in marked contrast to the TGV network. In Germany, this two-tier aspect was made very visible by last year's €9 ticket, which allowed unlimited use of local and regional trains, but not ICs or ICEs, for a month. This is now being made permanent, albeit with a higher price of €49.

tl;dr--high-speed trains were never introduced for the good of the planet but 'for the economy'. What have cyclists ever done for the economy?

Imagine if they made it a genuinely useful service and priced flights appropriately, how many flights could they cut?

Well, I don't think any meaningful action is going to be taken on flying in our lifetimes, I'm afraid. Anything that would make things better would involve 'less', which is a forbidden word.