1) I´m not saying it won´t work. We have Shogun 2 and its campaign Rise of Samurai is about previous more simplified period of time when even warfare was more basic. (no firearms,guns). But DLC for first and second age would be actually more like completely new expansions. Campaign maps more larger, scale of conflict bigger. I will speak about unit variety later but now I will just mention different scale of power. Way way bigger. Like Morgoth vs Sauron vs Sauron spirit. At one side we have like Elves at their peak strength, battling some Balrogs and millions and millions of Orcs.
2) Tolkien is like groundwork,base for all modern fantasy. It is quality superb material. That´s not question. Just saying that from that is point, other authors had 50+ years to produce some evolution over this basis. For races, units, characters..Like in Tolkien while we have Elves vs Elves conflict, we have just one race of Elves. In others we have like Night Elves, Dark Elves. (yes, Tolkien has Sundering, all different clans/branches with the little nuances between but he never went into splitting High/Dark Elves/Wood Elves as in Warhammer. Tolkien made the basis but never pushed limits. I´m not saying it is good nor bad, just a fact
) We have not just Dwarves but even Chaos Dwarves, Undeads are proper factions as are usual Vampires...and not counting crazy races like Skaven.
Getting back to unit variety. People were/are able to produce a lot of additional material especially for these mods. But that is exactly what i´m talking about. It is not contradicting lore but it is not directly from books. Like you cannot show me army book for Noldor army or Lake town written by Tolkien. And i´m not sure he would do one even if he could. ;-) May be the best point would be Comparing Hobbits, book and film. How many aspects were added into films especially for Battle of five armies. Goats, Chariots, Ballistas, Ogres, Trolls...
3) You are completely right about reaching heavens or even stars!
It is more likely I´m now sick with how Star Wars universe is being little ruined (Episodes 7+8+trailer for Han Solo..Rogue One was superb). The argument is more about not doing games for sack of doing just games. Because everybody can, that is not quite good reason to do it also....If they dare, then I hope for AAAA game quality. To put argument back to Tolkien/Warhammer. Warhammer gets three games, trilogy, three parts...whatever. And even with all DLCs and parts with all the the CA put into Wh1+2 I can still see some downfalls and missing some parts of lore,world,whatever like comparing now Beastmen to Norsca or Tomb Kings or just even comparing WH2 cora factions and their rituals to Wh1 core factions. We all have the perfect image in head how the game should be, what aspects must be in.....and even if i´m quite happy with CA and their Wh translation into games, one of best possible in history, still it is like coming little short of my expactaion which are unhealthy high....