Here are some discussion ideas I can think of off top of my head.
Discussion of events from specifc era as if we were in that time frame.
For example, during War of the Ring (Third Age)
We know Elves are real, talking trees are real, gigantic eagles are real, because we can go and see them at any point (although journey would be difficult)
but we have only heard of Valar, Morgoth, Numenor and such through loremasters and historians.
Also looking at events from different perspective should be interesting.
Lot of guess work needed for this one (due to the fact Tolkien only writes about Elves and occasionally Numenorians), but this should start some interesting debates such as were Numenorians as good as they claim? Is Gondor really true Heirs of Numenor or should that title belong to Umbar? Were Dunedains racist (not specist)? Are Elves are noble as they were portrayed (for Orcs take prisoners of War while Elves just slaughter every Orc for being Orc)?
And since we know Red Book of Westmarch was written by the Hobbits and copied by Gondorian scribes, and we also know original copy of that Book doesn't contain true story of how Bilbo found the Ring (although Frodo and Sam made other copies containing the true story and possible theories), what other 'facts' could have been distorted to suit the need of Gondor and her allies? Druedain's chieftain mentioned their people being hunted like animals, indigeous people of White Mountains are known to have fought Numenorians, Dunlandings certainly had good reason to hate Rohirrims, why did Harad and Rhun hate Gondor so much that they fought to the last man in every battle even after orcs fled? What was the full extent of the damage Numenorians inflicted on Middle-Earth for their precious lumbers? Were 'middle men' of Middle-Earth truly evil or did they have good reason for attacking numenorians?
If we step into mythical era, we can talk about was Eru good god, what were some of evils of Melkor that ended up making the 'music' even more beautiful (obvious examples being gallent deeds of Noldor, I think), were Valar good guardian of Arda, if we were to ignore what happened outside of Arda were Melkor and Sauron evil at heart, what would Sauron do once he conquered all of Middle-Earth, how strong are Ainur compared to Children of Iluvatar, etc.
Well that's more a mess than a list of ideas, but that's what I've got for now.
Edit: Also we can talk about more Game related contents. What were less known events going on during the time frame (Bilbo's 111st Birthday to Frodo's departure) or what would/could be happening during within those timeframe in various regions of Middle Earth and extraporate from there to discuss relevent characters and how it effected War of the Ring and such.