I think that hypothetically, a person could invoke the elimination of distinctions between legitimate and illegitimate children in civil law, and the fact that
neither the 1991 nor the 2015 decrees on titles mention legitimacy, to argue for construing the regulations in Delphine's favor if she is acknowledged as Albert's daughter. But Delphine Boël and her lawyers have on multiple occasions released statements asserting that Delphine is not asking for succession rights, titles, membership of the royal family, or even an inheritance, and even in the unlikely event that they backtracked, they would in a pragmatic sense require the consent of the royal family, the government, and/or the courts, none of which are likely to devote any effort to providing royal privileges to her.
As far as I'm aware, the only benefit that her attorneys have confirmed she would take advantage of, if her suit prevails, would be the right according to the civil code to adopt Albert's family name. But as that right was not established by the constitutional court until 2017, it cannot have been a factor in her decision to sue in 2013.