I am toying with a gnoll replacement (more along the lines of Runequest's broo, which operate in the same thematic space) and making it a playable ancestry in Shadowdark, although it would be one of the "uncorrupted" tribes, rather than evil demon-worshipping ones.
Doesn't Kobold Press have gnolls available as a PC race in their Southlands setting?
Correct. Specifically the Southlands Player's Guide.
There's a playable option for gnolls in DM Guild material for Eberron by Keith Baker. Exploring Eberron specifically, given they can run the gamut of alignments like most other creatures in that world.
Midgard gnolls are a martially-inclined race (+2 strength for main race, +1 to Constitution, Wisdom, or Charisma based on subrace) and their default race and subraces get a variety of things, usually related to surviving in a harsh land. Like advantage on scent-based perception checks, bonus speed when taking the Disengage action, resistance to fire damage and going for longer without water, etc.
Eberron gnolls have no subraces and are a bit more limited in being physical fighters (+2 Consitution and either +1 Strength or Dexterity). They get a bite attack, bonus proficiency in a hunting-related skill, and can bonus action move and attack whenever they reduce someone to 0 hit points or bite someone.
Both gnolls have darkvision 60 feet, but personally speaking the Midgard gnolls feel they can reflect a wider type of character concepts. The bonuses to Wisdom/Charisma are very nice to war clerics/paladins/rangers, they get double proficiency to certain social or survival skills under the right situation (like bullying someone obviously outmatched or weaker than you with Intimidation, or Survival when scavenging food and water). Eberron gnolls is good if...you like to bite people and want an easy means of a bonus action attack, I guess. But when compared to other natural weapon users like minotaur (shoving horns) and tabaxi (double speed) they don't have as cool features.
I've always had a soft spot for gnolls, though have never had the chance to play one. There was a brief phase in (I think) the 90s when, in the absence of half-orcs in the PHB, it looked like gnolls were being set up to be a new 'monster' PC race that didn't have all the baggage of orcs or goblinoids. David Cook wrote a novel to that effect I think - Soldiers of Ice. One of the better earlyish FR reads.
Hmmm, that sounds pretty interesting. Kind of makes you wonder about the D&Ds that could've been...