I don't think anyone has ever thought a living card game could be seen as the reimplementation of a boardgame. AH LCG just replaced the Call of Cthulhu LCG they had in catalogue back in the day.
I also don't think Eldritch replaced Arkham Horror the boardgame. AH had its course: a ton of expansions, and a nice blender at the end that was the perfect topping on a terrific cake. At that point expanding further was unlikely to happen: not in a conventional way at least. To go further, they should have gone a different way, and they decided not to do so. Eldritch is a different game, scratching a different itch, and having different problems than Arkham. Players in love with Eldritch will say it's the best of the two, while players who grew up with Arkham will say Arkham's a better game. Truth is that Arkham Horror: the boardgame is something that's very difficult to beat in terms of market: it came out with the perfect theme at the perfect moment. Now we have tons of games about the Mythos, and in general the hobby is quite a different reality from what it was when AH was released.
Truth is also that at some points these games collapse on themselves: there's just too much content and the "creative space" to expand further becomes narrower. Eldritch at the moment has 8 expansions, with stories covering the most remote corners of the earth, a gazillion AOs and Investigators, so, it has already given to its fans a ton of content. The latest expansion added campaign play which might have been a route for further expansions but that was also very much criticized for many reasons I won't enter into (personal taste or actual bad design, we could spend the night talking about this), and it was also the last expansion designed by Nikki before her departure from the company. So, the question here should be: is this enough? has the game told its story / run its course? and that's it. If there's more stuff that could be added and this reveals for the company more lucrative than pursuing other projects, we'll have more, regardless of LCGs or other boardgames.
And what exactly has this to do with Eldritch Horror? Or with anything else from the Lovecraft Universe? Of course you can do whatever you want for your private use but what is next? Luke Skywalker for Eldritch Horror? Aragorn and Frodo? Sorry, not for me.
Why did they only give us 6 improvement tokens for each skill!? Out of all the expansions we kept waiting for more but they never came. For those of us who regularly play 8 players this would be really helpful....
Well some of these are quite obscure, even I haven't heard of some of them and I read all works from HPL, many from Derleth and some from Howard (Who are Glaaki, Y'Golonac and Eihort e.g.?) but a far more important AO ist missing in this list and IS included in AH, Ghatanothoa. I still hope we will see him in a future expansion.