I run MOG under Squeezebox and it lets multiple clients access music simultaneously. This is a very nice feature because multiple family members have access to one account for only $4.99 per month. I have plenty of bandwidth out of my house to serve this up for all of us. Only catch is that Squeezebox (Logitech Media Server) is an odd duck. It uses a chair control kind of approach to controlling players and the mobile apps are flaky because of this model. Anyhow I love iSub and I'd really like to access MOG via Subsonic. Its definitely doable using openly available apis because it's there for LMS. Please investigate as this opens up subsonic to a huge new territory. Or even better if you could provide a plugin API then other developers could add MOG/Spotify/etc. LMS is actually totally open source you might even consider the same plugin api which would get you dozens of plugins immediately.
thanks