I agree, requiring 4-5 players for best results is a killer for most people and would seriously hurt player adoption. At a minimum they would need to also develop a good set of 2p rules so you could play it as a duel. A Game of Thrones is more or less like this now with two modes of play.
I don't know if the theme is a big issue or not. Personally, rival vampire clans is fine with me. Or rival alien civilizations. Or rival mafias. Or rival fantasy races. etc… You almost have to go out of your way to find a theme bad enough to be a stumbling block as long as the gameplay is good and the art is at least reasonable.
Now granted, FFG seems to have a preference for licensed themes since most of the LCGs are licenced theme games. Netrunner can probably be viewed as a conglomerate of whatever hacker and cyberpunk themes you're familiar with - it doesn't really have to start from scratch, and many other "generic" themes don't either. Call of Cthulhu is much the same, it's based on the ever-widening Lovecraft mythos but can also tie in with some general horror/magic/ancient evil/forbidden knowledge themes.
Plus, with a non-licenced theme game there are fewer limits as you don't have to worry about matching canon or introducing new concepts that may not exist in the source material. And, it's cheaper too
I'm less worried about the number of LCGs though. They had 3 for a long time, and the 4th one (Lord of the Rings) didn't ruin the others or suck. Then they had 4, and the 5th one (Netrunner) didn't ruin the others or suck. Then there were 5, and the 6th one (Star Wars) didn't ruin the others or suck. I'm pretty sure that number 7 or even 8 are probably going to be fine too. It seems like over time the top/most experienced LCG designers are helping create the new games and get them off the ground while the older games are gradually transitioned over to newer designers after a suitable joint-control tutoring period.