Hound attacks serve an interesting purpose in DS/T and spice up survival by adding tensions and a bit of randomness. They are one of the first big threats that a player faces and are scary at that.
A veteran player however might find them a bit tedious after some point. They are tuned in a way that they increase in difficulty mainly by adding frequency but also to their variety and pack size. I think the former merely makes them annoying and but the latter makes them more interesting, challenging and even valuable.
One theme that is consistent with hounds is the sometimes so called elemental hounds, having unique perks that increase their power and reward, by dropping blue and red gems respectively.
I think one could expand on this theme to make hound attacks more powerful and rewarding (per attack) while decreasing their frequency.
Each yet unused gem color could represent a different hound type. They would have more powerful perks while granting a chance to drop their respective gem color.
* Purple is the color of magic and insanity. Purple hounds could simply have a stronger insanity aura and similar stats to elmental hounds. When they explode, they deal a bit of AoE damage that drops sanity for a moderate amount.
* Orange is the color of sloth, free mobility and transport. These hounds could possibly teleport away from the player after being hit or even to the player to close the gap. This would make fights more chaotic and challenging.
* Green is the color of cheating, they are used to create something from nothing. These hounds could spawn two additional regular hounds after being killed. This would incentivize players to kill them last.
* Yellow is the color of speed and light. The most powerful gem in DST could make so yellow hounds are charged with lightning, similar to volt goats. When attacked without wearing insulation, the player would be stunned, incentivizing additional preparation for hound waves.
Also the orange, green and yellow hounds would have increased stats, such as +100 health and +20 damage per attack. The very much increased difficulty would warrant a significantly lower hound wave frequency and a well-tuned spawning rate for each of the variants.