Well hopefully we will get to see at least something in the next few months, because if they are just seeing if the Lumineth will be popular enough to justify adding more units or not, then they may have just doomed the faction from the start.
If they are basing popularity on how many player use them Competitively, I can defiantly see this faction struggling. Not because there units are rubbish because they are very viable like you said, but because of the shier lack of options. Meaning many builds will be in readably similar to each over, making it relatively easy to counter them.
If they are seeing this based on sales alone, again I’m not so sure, because of the small selection available. I could be wrong though on this, but personally, I don’t really like factions that are limited to just one stile of play, like the fresh eaters, bone reapers, and so on.
I think these Guys will have some help from GW despite poor sail though, since these are supposed to be one of the main factions of Age of Sigmar, weather that’s enough or not....