I don't think anybody else has posted this yet.
According to this report: http://www.railjournal.com/index.php/high-speed/thalys-to-launch-low-fares-paris-brussels-services.html
Thalys are starting a new cut-price service Brussels - Paris. The disadvantage is, it uses the "old" line and takes 2h 15min instead of 1h 22min. You can choose, save time or save money.
Correction: Booking is on the website here: https://www.izy.com/en/homepage