It'd be really cool if we had body type options, even just a couple - the one we have now, and an option for a wider/heavier body type. All clothing items wouldn't need adjustments right away or anything - just start out with adding the body type variation to custom wearables, so the artist would submit a version for each, and new items released on site having these variations as well, and over time you could slowly add the variation on to older items as well, released a few at a time.

If you're talking whole new bases, then yes, it would be unlikely, just from a logistical standpoint. Right now, it's fairly painless to edit a top item for male or female. It's just the waistline (sometimes) and a small area in the upper chest that requires a bit of re-shading and editing linework. Most of the time, a single image works for both bases' bottom half. So for a single wearable you have 2-3 images total: item, male overlay, female edited overlay if applicable. The edited version of an overlay is also worth less since usually most of the original can be re-used.

Let's say that this was a new fat avatar base and it passes for male or female:

As you can see, the only types overlays that would get away with a simple edit would be sleeveless tops that don't extend too far down the body. Everything else would essentially be drawing a new item. That puts single wearables now at 3-4 images minimum: item, male overlay, female overlay edit if applicable, fat overlay. That's going to add up for the site once you get to recolors, and especially since the fat overlay would need to be the same value to us as the non-edited overlay (because it is a whole new image rather than a simple edit.)

And that's just leaving it at a single new base. What if that particular base isn't fat in the right way? Some people are heavier up top but they don't have thunder thighs. Some people are thicker in the legs but they don't have bingo wings. And then what about buff bases or thin bases? And m/f versions for those?

It's unfortunate that we can't offer those body types (and that we didn't start there at the beginning) but it really does come down to logistics rather than laziness or discrimination. It'd be fantastic if we could do them! But we'd probably end up getting less of EVERYTHING (including wearables!) because of the time spent on it.

That all being said, items with built-in base edits could work (like the maternity shirts) but then you run into the issue of "Does anyone want to have to wear this specific shirt to be fat?" or "What if the skinny people also want this design?"

This was pretty much denied in 2018, from Fat avatar items.