You dodged the greatest question: Do goblinoids can mate AND produce offspring between the different subspecies?
— Daniel Balard (@danielBalard) August 1, 2017
That's not a question specific to Eberron, and I don't know if it's been answered in another source.
— Keith Baker (@HellcowKeith) August 1, 2017
My assumption is NO. Goblins & bugbears are different sizes; we've never described hybrids; & we've called out goblins as fast reproducers.
— Keith Baker (@HellcowKeith) August 1, 2017
But I don't know if other sources say otherwise, and I haven't considered the value of alternatives.
— Keith Baker (@HellcowKeith) August 1, 2017
In eusocial species you often have a "queen" that can produce offspring of any caste. So that's something someone could explore…
— Keith Baker (@HellcowKeith) August 1, 2017
… but it would be a pretty dramatic thing to introduce.
— Keith Baker (@HellcowKeith) August 1, 2017
I believe Dragonlance already established this capacity with the setting’s Half Goblins (filling the role of Half Orcs due to the setting’s lack of Orcs).
That being said if I were to toy with the idea, I think a race brought about by blending the blood of Hobgoblins and Elves would be especially provocative in Eberron.