Well that's really quite tricky, isn't it? I mean, you save a whole lot of energy by using an extra click rather than a mouse move, plus literally milliseconds of time saved too.
Having an obvious Edit link to edit titles is hardly technical, certainly less so than an unobvious double click which is just poor UI.
What many threads? I see just this one thread requesting it and only two people have commented. No-one else has liked the suggestion in the first post. Therefore I'd suggest that there really isn't the demand for it.
What this is more about is a small number of admins coming from some forum software that uses the unobvious double click edit and wanting things to be the same on XenForo. Well, it's not the same and for good reason. Hopefully XenForo will stick to their guns and not implement this bad UI request.