There is no valid reason whatsoever for Assange to not have signed something with his PGP key (you don't "release the key", you "sign" something with it). It is a nearly effortless endeavour. Allow me to highlight some obvious shilling:
If the key was compromised, he would state that fact. The key being compromised does not in any way affect his ability to sign something with the key, it only means a third party could potentially sign things as well. The appropriate thing to do would be to sign a message stating the the key is compromised, thus proving he controls the original key, and invalidating all messages signed with that key thereafter. A third party who has the compromised key would not sign a message stating it is compromised, because it would do nothing but save Assange the time of doing so himself. Bottom line: Even if the key was compromised, he would still have access to the key and should sign a message with the key declaring that fact.
Another important fact
Assange has never given an excuse for why he has not signed something with his key, he has NOT stated that it is compromised. All questions in this regard are deflected and ignored.
Scenario A
Assange is alive and has his PGP key. He could prove in less than 15 seconds that this is the case by signing a message with the key.
Scenario B
Assange is alive and lost access to the key. This is a bad scenario, because if he announces this fact we would have to take it at face value that he is telling the truth. He would need to have a very good explanation and explain how he stored the key and how it was lost. This scenario is very unlikely given how clever Assange is (he would have stored his key with great skill).
Scenario C
Assange is alive and has his PGP key, but doesn't want to sign anything for some arbitrary, unknown reason. This is very uncharacteristic of him, and the motives for this scenario are unclear.
Scenario D
Assange is dead, missing, imprisoned etc. and his adversaries have assumed his identity. Assange destroyed or hid his PGP key before this occurred, or the key cannot be foun or isinaccessible to the adversaries whom have assumed his identity.
This scenario is in all honesty more probable than Scenario C, when taking into account no other facts about the circumstances and only analyzing Assange's past behavior.
In this case, the adversaries would never be able to sign something with the key, it would be impossible, so they would need to simulate Scenario B or Scenario C as an explanation.
Scenario E
Same as Scenario D, except the adversaries do have his key. Why they would not sign anything with it is unknown. One possible explanation is that they would allow people to complain for a long time that he hasn't signed anything, and then sign something and say "I told you it was me and that I'm alive, now never question me again you stupid conspiracy theorists!".
Scenario E_2
Same as Scenario E except that the adversaries impersonating him obtain his key using some kind of cryptographic reverse engineering or cracking. If this were the case, it could explain the long delay time in signing something with the key, assuming their process is extremely computationally intensive and say, for example, required the resources of their most advanced secret computer technology to crack.
