I don't know much about LotR lore so I can't comment on that, but I would love to see new products and mechanics for the game, being them official or fanmade. I'm relativelly new to the game, so maybe some of those have already been done, if so, I appologize.
1-. New card type: Havens . I agree with Gizlivadi that there should be positive locations to play and deckbuild around. There have been some fanmade atempts, but I would like for the devs to try to figure them out.
2-. New card type: Agendas . This has also been done by fans, but I thorougly enjoy the deckbuilding options that they bring for games like AGoT 2.0 and would like to see similar versions for LotR. Something like if your heroes share a trait/sphere, you get X benefit and Y penalty.
3-. The revival of Treasure cards. I know that they were transformed into Boons and Burdens for the LotR Saga expansions, but what I would like to see is a new mechanic that works around the scoring system/victory points. My take on the Treasure cards would be similar to the loot system of RPGs. Everytime you defeat an enemy/explore a location, you place one random card from the loot/treasure deck on the victory/loot display (separate them to avoid interactions with existing cards?). At the end of the quest, if the players were successful, they as a group can buy X victory points worth of Treasure cards. They can add them to their decks for the rest of the campaign (see below).
4-. New POD product: Saga/Campaign decks . A deck of 20/40/60 cards for each cycle consisting of new Campaign cards, Boons and Burdens to tie each quest together as a Saga, and Havens, Treasure cards, and Agendas to improve the thematic experiense. They seem to be willing to revisit old quests with the nightmare decks, so there's already a precedent. This new Saga/Campaign decks could attract a whole new bunch of players that were underwhelmed by the lack of campaign (and progress) in the base game, and have the potential to increase the replayability of the cycles.
5-. Revised core set . The core set could benefit from a revised edition with an improved rule book, a new reference rule book (like they are doing for every new LCG) containing all the new keywords, word descriptions, action timings and the FAQ entries that are exception to the rules; and revised versions of underpowered/overpowered the cards and distribution of the cards. A POD conversion kit could be sold separatelly for the old players who already own their cores.
This has already been done by the community on several occasions, but I would like for them to make it official. They have done revised edition for other board games and they have no issues on updating the errata cards on future printings.
6-. Tied to the point above: Improved solo rules . The solo gamers are a huge part of the player base, however, the official rules don't cater to them at all. It's obvious that the game is designed and tested as a 2 player co-op game which can make the solitaire experience not so great/balanced. There have been some attempts by the fans (the Fellowship variant on BGG comes to mind) to improve the expeirence. So official rulings in the new rule book wouldn't hurt. Adding new game variants in it wouldn't kill me either.
Will update when I have something else to add.
I hope you stay tuned to my 'Road Goes ever on' blog?
It ties in directly to many of your points and I'd love to hear your opinions on my versions of solo rules, havens, modified early cards etc.