At $5 a month, it appears to have been unviable.
Here’s the closure statement:
We regret to inform you that ClassicsOnline will go offline from 31 January, as our technology partner will cease operating the platform used for ClassicsOnline. Since customer support will be terminated, your subscription will cease on 31 January and the site will be closed down until further notice.
ClassicsOnline has been in operation since 2008 and we believe strongly in an online quality service dedicated to classical music. We now plan to develop a new ClassicsOnline, using different technology and listening concepts. We cannot give you an exact timing for its launch, but we will keep you posted.
Naxos started the high resolution service two years ago with ‘over 80,000 albums … from hundreds of labels including: Harmonia Mundi, Sony Classical, BIS, Chandos, Naive, Naxos, BBC Legends, LSO Live, Pentatone, Ondine, Delos , Signum, Hungaraton’ They charged $15 a month. Last month they took all non Naxos labels off the site and dropped the price to $5.00.