I might be wrong or it might be my ignorance. Isn't this issue of seeing the forum down became more prevalent after the Bitcoin mixer issue. I mean it is more frequent and long lasting before the mixer got down by the FBI.
Which mixer are you referring to? You need to be more specific, given that there have been multiple mixer sites shut down by the FBI/Europol.
But, I fail to see the relevance to the issues with the bitcointalk hosting server.
I think there is something wrong and I feel the admin should have two urls. One .org and the next should be .onion.
And what if the cause of the problem lies on the hosting side, as theymos has already mentioned? How will having a .onion mirror domain help in that case?