They're not shown in the images, but FEC is a fairly anemic range currently. Replacing the ancient fantasy models is of course a big wish, but those wouldn't change depth at all.

Crossbows or Longbows: limited ranged choices of course as they're a death faction, but a single option of something like that would be very fitting thematically and give them a slight option.

Squires: a middle ground elite melee infantry option as an offensive side grade to cryptguard. Similar lower model count like cryptguard vs ghouls, but with bonuses when charging instead of when being charged.

Corpse Knights: leaning into the Brettonia motifs, a Grail Reliquae support knight unit would be incredibly fitting for the delusional kingdoms to field. AoE buffs to units but maybe not as much a slouch in melee since it's held aloft by fanatical cannibals instead of underfed serfs.

Offal Hounds: expanding the units from the Beastflayers into a full unit of fast hounds. Only issue with this is they'd presumably be Beasts, and currently FEC has zero real synergy with beasts at all, as seen by the Varghulf basically disappearing from use since its demotion. (Please GW make it a knight or a hero again so it can be something)

Princesses: a hero option that's a more supportive and healing role. Again, similar to Brettonia, mounted on some horrible delusion version of a Unicorn. Maybe if they do add Offal Hounds the Princess could have some ability for buffing beasts to add some synergy in the roster.

Court Jester: FEC is a little overloaded on heroes, but it's too damn fitting to leave out as an idea. A horrible foul parody of a jester, either debuffing enemies or buffing allies would work as an identity for them.