Alesis owners already get the Dark Mahogany pack for free, whereas it will be a paid pack at launch. Everyone will get the Core Library for free. Other packs will be paid (cheaper than existing BFD packs!)
One of my future goals is to ensure compatibility between existing BFD3 packs and BFD Player, and I’m looking into the feasibility of that now. It requires a lot of content upgrade work, so it won’t be something that happens immediately.
In essence, BFD Player will eventually have access to an entire universe of drum sounds, preset packs, and groove packs.