Are they a particularly popular faction it Total War? I saw quite a bit of them (via YouTube videos) upon their release, but much less so recently.
Well, the Khemri TV memes and Settra's enduring cult status speak for themselves
In terms of popularity in Total War, this survey from the Total War forums done in 2019 ranks Tomb Kings technically 2nd in terms of the most popular faction lorewise, after High Elves, Dark Elves and Dwarf all ranking joint first. People at least appreciate how beast they are in the setting.
https://www.surveymonkey.com/results/SM-PHVQK8DJV/
This survey from 2018 with regard to the most played faction ranks Tomb Kings middling:
https://strawpoll.com/3g947ygw/r
Can't understand how f*cking Empire is the most popular, given it's a FANTASY GAME and humans are boring in a fantasy setting (particulary those humans with their silly German names and even sillier hats), but I digress. Tomb Kings seem to have more popularity now Warhammer Total War's hit than before it arrived, because before that they were pretty low down thanks to GW shitting on them all the time. I certainly think that if they were reborn in TOW, they would be more popular than before, particularly if they were given better rules and given the respect they deserve.
Some of the existing TK line is extremely viable, but others are quite dated. Maybe it will be a combination of the two strategies.
To be honest if they were going to update the old 6th Edition stuff, they'd be far better off doing much of it in plastic given it's the Core Units we're mostly talking about - players will be buying many boxes of these so will need them to be more affordable, plus customisability is always wanted for such units, which plastic kits give out in luxury while Forge World provides next to none.
Knowing GW they probably will make them in Forge World for the PROFIT but that certainly wouldn't be an ideal scenario for the customer. I can see support from TOW draining if GW makes this decision. Though to be fair, if GW keep up the horrendous price increases for basic core unit plastic kits we've been seeing for the past year, they'd get just as much PROFIT out of making an updated plastic kit as a Forge World kit...