IMO, it's still asinine to give an ultimatum like that. If the rabbits are a deal-breaker, then man up and say "I want a divorce" instead of trying to make her be the bad guy.
We've got 9 pets - 2 cats, 4 gliders (two of which are a breeding pair, they just haven't started breeding yet) and 3 bunnies... it definitely takes time to care for them all and make sure they get enough attention, but it's extremely doable without having to neglect your significant other (and heck, if your SO loves animals as well, you can spend time with them and the animals at the same time - Jay and I do that daily in addition to having plenty of time for ourselves without the pets). Given that it sounded like she doesn't have a job other than her work-at-home business (which she started after kicking his butt to the curb), she'd have all day while he was at work/the kids were at school to spend time with the bunnies... if she also spent most of her time with them when he was home, then that was probably because they were better company
. Also, the article indicates that while she had multiple rabbits when the ultimatum was issued, she didn't actually get up to 11 until after he was gone.
If you have to get rid of your pets to "earn" someone's love, they're not worth having anyway.