The French speaking organisation GR Sentiers announced this new GR17 already a few months ago. Lately, attentive hikers could notice the markings being put in place. The new long-distance trail will be known as the "Sentiers de la Lesse et de la Lomme". Technically it will be two trails, joining at the confluence of the Lesse and Lomme rivers in Éprave. One part follows the Lesse rivier for 105 kilometers between Ochamps (its source) and Anseremme, where it flows into the Meuse. The second part runs along the Lomme between Bras and Éprave.
Be aware that this trail is not replacing the well-known "Entre Lesse et Lomme" loop of 78 kilometers. Actually both the GR17 and the ELL will meet each other on two occassions for only a short while. The topoguide of the GR17 has just been published. In it, apart from information about the trail, you'll also find a description of 10 loop hikes in the area around some of the tributaries of the Lesse and Lomme rivers.
The guide is available only in French on the website of the GR Sentiers: https://grsentiers.org/topo-guides/188-gr17-la-lesse-et-la-lomme-par-les-gr.html