And good luck to them too. It remains to be seen how this pans out - I'm sure there will be plenty of competition on the main routes to and from Paris. Not so sure about much changing on the regional lines, or connecting the (relatively) small provincial places, except where the competitive Paris based services provide them as a by product. Could even be worse due to the loss of cross-subsidy funding. I don't think Italian or Spanish regional services have benefitted much if any from OA competition. Returning to the OP, it will quite possibly result in competitive (and more) service through the Channel Tunnel, but I suspect that this will be on the existing Origin and Destination pairs rather than anything new, and more Lille to anywhere else connecting service probably not. Remains to be seen of course.
Without the safety of the cross subsidy SNCF or the French political class would be forced to go back to the first principles of running a railway. It may be that they'd be forced to think how to capture markets such as St Etienne - Colmar, Valence - Sarrebourg, or Bourgoin-Jallieu - Calais onto rail. It's not even for lack of trying, SNCF actively makes such journeys as awkward as possible (try changing onto a TGV from a TER at Lyon Part Dieu).
Yet it'd be almost laughably easy to sort this. Credit where credit is due - under regional PSOs the TER services into Lyon and Mulhouse - Strasbourg have become clockface and frequent. All it takes is for Lyon - Strasbourg and Lyon - Lille - Brussels to be clockface two-hourly, which would represent the most marginal resource uplift from the current timetable imaginable. Then just time the Paris - Lille - Calais/Dunkirque splitters at two-hourly intervals to connect into the Lyon - Lille runs. Then all those O-D pairs would be served with consistent journey opportunities with consistent journey times throughout the day and you've created a brand new rail market.
The next step would be to introduce an equivalent LENNON/ORCATS/TSA system as a basis for commercial decisions and subsidy calculations. This way SNCF can't hold regions over a barrel for demanding reimbursements for services they would commercially run anyway.
Do these things and I'd be surprised if they don't soon discover those 2-hourly connections should become hourly ones.
In my experience, E* have always been very helpful in rebooking on subsequent trains in these circumstances (happened to me on various occasions and never had any problem), although presumably as with the airlines this could be a problem for large volumes at peak times. The capacity is the capacity, and the airlines generally cope in a similar situation.
Here we are, back to the absurdity of talking about a railway system in aviation terms. There is a ridiculous number of hurdles -
- The biggest one - being outside of Schengen. The issues are two fold. If Amsterdam - London services could freely pick up and drop off passengers at Antwerp, Brussels and Lille we'd probably be looking at an hourly service already. Secondly we are at the mercy of border control capacity and staffing level consistency at London, Rotterdam and Amsterdam - if that constraint is removed a two-hourly service may be viable
- Channel Tunnel security - I've never got to the bottom of this one. Cars and coaches driving onto Le Shuttle don't go through any security. Is station security an actually mandated thing?
- Eurostar's SNCF DNA
The most fundamental hurdle is not going to go away any time soon. I'm not just interested in railway outputs - I'm interested in socio-economic outcomes. 'Doubling the number of destinations' is an output led soundbite to the point of pointlessness. What's important is an increase in passenger volumes travelling to a more diverse range of destinations including through interchanges - and I think diversifying viable end destinations will be a crucial element in raising the volumes - the point-to-point markets are ultimately finite. With border arrangements limiting direct services to Paris, Brussels, Rotterdam and Amsterdam, growth has to come from interchanges. This comes back to the point of making Lille a Takt node. It's one of the only available instruments.
How much demand is there? How much is being catered for by air? (the train journey from Paris to Milan is very long 7h or so, with the flights so much quicker) International journey demand is usually quite different to national capital/main city to provinces demand. Some countries have a greater cultural affinity / historical connections than others.
There's enough circumstantial evidence to say the Paris - Frankfurt/Stuttgart demand is suppressed - high fares, frequency accounts of trains selling out. And I stand by my rule of thumb that if a corridor operates an 'SNCF' frequency (e.g. sort of two-hourly but with gaps) then the actual commercially viable market is at least the equivalent all-day frequency (so clockface two-hourly all day). In the case of Paris - Frankfurt/Stuttgart the main supply-side blockers are actually German infrastructure. I fully expect this side of Germany will be among the earlier adopters of the Deutschlandtakt.
Paris - Milan and Paris - Barcelona probably aren't sufficient competitive to carry any more than the existing 'ardent rail travellers'. I'll wait until all the planned HSLs are built before blabbing on about takt. In Barcelona's case at least wait until Sagrera is complete.