Well, if we are talking about lore-friendly options, almost every race wields shield & spear. Dark-Elves have Dreadspears, High-Elves have like 11 different units from chariot-riders to knights to the Lothern Sea Guard to standardized infantry, Wood-Elves have the Eternal Guard and Glade-Guard, Norscans wield it, Lizardmen wield it, Empire-Folk wield it, the Brettonians wield it, the Skaven wield it, the Undead wield it… really the only races that don’t are Dwarves and Orks and it’s because they’re weird.
There’s almost no such thing as a non-lore-friendly spear & shield.
Foot-Knights aren’t often pictured using spears, but I could see it. I mean, spears are just a good all-round weapon. Not necessarily lore-friendly to Warhammer, but if Kruber said to himself “I want more reach and to poke instead of slashing so I don’t get in my ally’s way,” who are we to deny him?
Mechanically is a different point entirely. I’ve got no input there because I always wield the weapon I want to wield, not the one that operates best-in-slot.