For return services Antwerp would need to install border checks and a security hall, something which will take a while to install.
According to the article in the first post, there are no plans to install these facilities at Antwerp, presumably for the reasons listed by rvandeborgt
I'm not sure where you could fit in border controls for a reasonable price and also seal off a platform without hindering other trains.
Good new but why only on the outbound? After some time in Antwerp I'm sure people will want to go home again as one way traffic cannot be that big of a market.
I'd add that Eurostar has a history of offering certain routes directly in one direction only, including:
- The south of France services (were direct from London, Lille shuffle on the return)
- Eurostar snow/ski services (direct from London, Lille shuffle on the return)
- Amsterdam/Rotterdam (when they started, they were only direct from London, and used a Brussels shuffle on the return)
And Lille to Brussels/Rotterdam/Amsterdam is only offered in that direction.
Overall, I would say that it is customer-friendly to serve Antwerp even if only in one direction, especially as it likely doesn't extend journey times at all