There's no info yet on the price, the number of titles offered, the name, or even the launch date, but one detail that is being bandied about is that this service will charge a monthly fee to let users read an unlimited amount of ebooks.
There is also speculation that the selection could be diverse. The 2 publishing houses make up a significant part of the Dutch book market, and since they are launching it themselves it's likely that they will try to include as many of their titles as possible.
Should this service launch it will be at least the 10th Spotify for eBooks spread across 6 countries, including Brazil (Nuvem de Libros and Oi Bookstore), Denmark (Mofibo and Riidr One), Russia (Bookmate and MyBook), Spain (24Symbols), Germany (Skoobe), Netherlands (Yindo).
And of course there is the Kindle Owner's Lending Library, the single largest service and probably the most successful. The success of the KOLL seems to have smothered its English language competition, with Flatleaf and Afictionado shutting down before they really launched and Bilbary abandoning plans for ebook rentals. About the only English language "Spotify for eBooks" still in the running is Oyster, which launched last October but has yet to open to the public.