Kale is okay for him to eat everyday but I would keep trying new stuff to see if you can find something he likes. The HRS’s bunny safe veggies list might give you some ideas:
http://rabbit.org/suggested-vegetables-and-fruits-for-a-rabbit-diet/

Hey Lainie, I give my boy Kale (around the size of my palm) every day with his other veggies (around 1 &1/2 cups full). Tonight it’s kale, cabbage, red lettuce, parsley, carrot (only the top and bottom from cutting up our dinner) along with a bit of broccoli and cauliflower. Whatever Henry hasn’t eaten by morning, I throw out (it’s warm/hot here so it gets yucky overnight). Most nights it’s gone, sometimes he eats the leftover’s in the morning, and on occasion, I do throw some leftover’s out. Maybe give Bentley a smaller amount of kale, and if he’s hungry for fresh veg, he’ll eventually eat what else is on offer. But yer, the only time Henry doesn’t get his small amount of kale everyday is if the veggie shop has run out. And get this – I had never even heard of kale till I found out about it on BB. Because of what I’m thinking of cooking for dinner later in the week, you can add bok choy to the mix, ha hah! I do buy specific veg for Henry, but a lot of it (except the no no’s of course) is whatever we eat for dinner. Keep in mind, maybe Bentley doesn’t like something on offer? My boy hates zucchini (dam, we eat it most nights), so I don’t even put it into his bowl anymore. Thankfully (for me) we didn’t get Henry till my kids were grown up – I can imagine them saying when they were younger, “Henry doesn’t have to eat his zucchini – why do we have too?” – ha ha hah! Too funny…..

I’ve found that my buns go through phases. One minute they like something, the next minute they don’t. Maybe just give him the kale for awhile and then start offering him something new. Sometimes the fact that it is “new” is enough to entice them.

Do you give him whole leaves of veggies, or tear them into smaller pieces? I’ve found that when I tear and mix up their veggies, they’re more likely to eat at least some of their less-favored ones.

I can still see that they’re disappointed if the dish doesn’t have any kale though

I used to feed my girls a kale mix almost every day but after Pippin had been on antibiotics and then had runny poop, kale wasn’t helping her situation at all so I had to switch them to romaine and collards and various other lettuces. Just keep that in mind, that at any point your bunnies digestive system may decide it doesn’t want that certain veggie anymore so just try and switch it up!

I’ve heard that kale is high in calcium, and a diet too high in calcium can cause problems for your bun. Mine like kale too, but I think excessive amounts might not be the best. Have you tried cilantro? My bunnies really like cilantro You could try introducing other greens one at a time… and kind of like kids, if you keep offering them small amounts of new greens eventually they might decide to try it