Access charges are the same for all operators in Belgium, SNCB and others pay the same. So arguing about that un court wont be easy.The problem are indeed the access charges, which, just like in France, make it prohibitively expensive for non-incumbents. The EU should do something about that.
But Brussels would be a good market. Especially if they time the train to have good connections with Eurostar and sell through tickets.
Changing in Köln and using Thalys has currently a few disadvantages. DB is no longer selling Thalys tickets for example, and in the last Thalys from Brussel is to early, meaning that you have to hang around Köln Hbf for over two hours late at night...
Poland still has the Paris-Moscow link 3 times a week plus other trains to the east.It's a pity there are no night train connections anymore with Poland. Wasn't PKP interested to run Rhein/Rhur - Wwa/Wroclaw/Kraków, or too much competition from Wizzair and Ryanair?