With many things it's just a matter of keeping offering without pressure and one day they'll have a taste or increase the amount they will have of something.
Whilst I don't pander to pickyness with foods I will happily adapt many things so that DS is happier and there are some things which he truly does not like, never has, he might one day though so I still give the opportunity.
For example he has also never liked much in the way of potato BUT he did like roast potatoes with herbs/spices on during cooking and eventually over time without the herbs too. He has over a long time tried a little more boiled potato but particularly if I give a little dip (ketchup or bbq sauce, or even just a bit of lemon or mint) it helps so what I've always done when we have mashed potato is to lift out a few boiled potatoes before I mash, toss them in a bit of mint and leave to cool for DS whilst I mash the rest. He did once eat a mashed potato ball (I rolled it in my hands) but didn't like it, he has asked to try some a couple of times and still not liked it.
Home made oven chips he will eat (any veg - turnip, swede, carrot, parsnip) so actually if he didn't like regular potato it woudn't bother me. Maybe try some of these different flavoured chips/wedges?
Rice is the same. He cannot eat it, just can't. The couple of times as a baby he had rice he vomited. I never expect him to eat any not even a mouthful but on occasion he will ask for a small try, he ate a little rice for Chinese New Year at nursery (they had a range of foods for snack) but declined the offer in a restaurant recently. I must admit that as a result I make rice less often, but when I do I just make sure there is another option for DS, a piece of naan or chapati, a pita, noodles or just a piece of regular bread will do. I would say your DS is much closer to accepting/eating rice than mine. You can make sticky rice which is easy finger food. Or can he just have the rest of the meal without the rice part?
Meat has not been a big favourite here either. Slow cooked meat like pulled pork (in a bbq sauce) or crock pot pork and apricots he will be happier with. He once ate almost a full lamb shank as it was so soft and in a sweet sauce. so I suggest slow cooked meats.
Also meatballs or meatloaf which has breadcrumbs mixed through makes them much softer which may help.
Again dips helped here, he is more likely to have some meat if it's in a sauce or gravy or has some dip on the side.
With chicken in particular it was a funny introduction. He'd been to a birthday party and tried crisps (potato chips) for he first time, of course he loved them, next time we had roast chicken I gave him a piece of highly seasoned (not lots of salt but lots of herbs, garlic powder etc) and very crunchy chicken skin and told him it was like 'wet crisps', he tried it and loved it. So for a while he only ate the skin, then I started to leave a little chicken on the skin and a little chicken on his plate which he began to eat.
I do notice with mine he likes quite strong flavours and i wonder sometimes if the dislike of potato and rice is partly due to it being bland as well as a texture he can't stand.
I would just keep offering the chicken and he will eventually eat some.
Don't know if you like fish but I also found DS preferred stronger flavoured fish such as mackerel and sprats rather than cod or haddock (although he will eat those crumbed like fish fingers, so long as the crumb is well seasoned).