My sister and her husband bought and built a home in the new Cotino (Disney) development in Rancho Mirage, which is basically across the street from Marriott Shadow Ridge, and were one of the first to move in earlier this year. I have been there several times. Yes, there's a huge lagoon with paddleboats and the like. It's a very nice (and pricey) residential community. I doubt very much whether day passes will be available to the general public (membership in the Cotino club is pretty pricey, $20,000 initiation fee plus $11,000 per year, but those may be available to non-residents at some point.) Edit: it seems that eventually, there will be (paid) public access to a shopping and dining area to be built on the opposite side of the lagoon from the residential neighborhood. Those amenities and the public access do not yet exist.
I do not believe there are plans for a hotel, this is a residential neighborhood.