I have used both boards in the past regularly and LH and LX forums are the two I checked even if I am on the road and have to use my PDA.
As said by others the style of discussion is quite different in the LX than in the LH forum. It is more convenient and you find the topics you are looking for faster, as there are the most time only one discussion to this topic as three or four in the LH forum – and this even without a moderator. On the other hand you should also be aware of the fact, that LX has still in my eyes a better customer relationship and as far as I know they are monitoring the board.
The LH forum is in the need of a moderator and the job is done very good by Kiwi Flyer, but the of topic discussion becomes more and more disturbing, if you are looking for information or give information. Many post are not appropriate for a forum but for a discussion via a Messenger Program or for Omni. This is a general problem and not related to the LH forum but is more or less not existing in the LX forum.
On the other hand there are a lot of topics which are not covered in the LX Forum. And I personally think it would even make sense to make a own subforum for discussions concerning Austrian, LOT, Regional Members. The problem with LH is that the board is to big because the number of airlines using LH Miles and More is to big. So if you are looking for information about Austrian you have to look in the LH board which makes no sense and it is difficult to get and give information.
So a merger of both forum would be the worst I could expect, creating a sub forum would be the best thing in this situation. And if you open sub forum like suggest for Austrian / LOT / Regional Members I would be “a very happy customer”