One of my first concerns would be that this would build in a very easy way for a government (probably the US government) to compel Tor to add in a line of code that says "If it's this hidden service key, block access."
After all - it's a stretch to say "You must modify your software to support blocking things"[0] but it's not so much a stretch to say "You already have the code written to block access to things, block access to this thing."
-tom
[0] The OnStar legal case notwithstanding