If we do that it will be locked when someone is replying and sharing some useful information.
What about if we set a timer and in the mean time we don't get the solution?
I am not saying that its a bad invention I really appreciate your work but if you want to be perfect then you should lock your thread manually.
What is the rate in $ you are selling?
You can unlock the thread, which was locked. As an extra feature, timer could be dynamically modified in the meantime. When you have several threads, maintaining them could become very difficult and no one wants his thread become a spammer hell. I am sure, you know the situation when people are saying the same thing again and again...