I actually intended to do this at some point as a spinoff of my Necromunda mod, but I'm glad someone else has taken up that responsibility. The way I planned to handle the breeding problem was to make two major castes, boyz and gretchin (grots being used as the child name for Boyz and their subgroupings and snotlings as the child name for gretchin.) All grots would have the [FEMALE] token and all boyz the [MALE] to satisfy DF's requirements. You could also use the localization patcher to change "wife" to "grot" and "given birth to" to "has tended the growth of" or whatever works. I also wanted to make a variety of castes to represent Ork castes like mekboyz, nobs and wyrdboyz and the like whilst limiting the basic castes to only certain skills (no engineering except for meks, etc.)
If you want to use graphics, you can also easily use skills rate tokens to limit grots to certain skills and boyz to others so that they never use the same sprite (putting in a natural skill too while you're at it to guarantee no peasant/recruit sprite overlap or grots/boyz getting the wrong sprite from embark skill assignments.) Speaking of graphics, I might be able to do some if you want, though I've been kinda busy lately.
The bigger lore-related problem I had with figuring out an Ork mod was how to justify orks muckin' about all day instead of fightan and winnan. But the idea definitely has potential. Feel free to lift anything you like from my own mod, by the way, it's got a lot of 40k stuff in it already converted to DF.