Another source of good minis and faction/army ideas is some of the other FFG games as these may have units that suit armies you may wish to add- LOTR Journeys in Middle Earth and its expansions (I've fallen for the monsters in Shadowed Paths already, seems to have a couple of spiders that could go well with an Ariad spider army and some other creatures/pieces that could be useful for all my ideas!) and the Arkham/ Mansions of Madness lines have some options for horror/other factions.

https://www.fantasyflightgames.com/en/news/2020/1/28/shadowed-paths/

Having talked about 'Descent to RWM' ideas Path of The Serpent from MoM has potential to build up a wyrmy/snakey/lizardy army of some sort. This could be good for an alternative army for the beastmaster as it feels like he fits this idea really well- and bringing back the Mistress of Serpents from d1e if you can find a suitable mini, along with some naga (which if you have the D1e and 2e figures which are different sculpts could be quite a pleasing Mennaran army)

https://www.fantasyflightgames.com/en/news/2019/6/24/path-of-the-serpent/

Any other current FFG/Asmodee lines that have potential?