I just love hearing about everyone's experiences here. Your son sounds wonderful!
My DD does not approach this LOG but I will tell you a couple of experiences that we have had.
At about 26 months she had quite a few words that she could recognize but was just starting to sound out new words to read. She was intensely interested in letters in every place she could find them and was trying desperately to read. She knew the sounds and would try to decode a word but was generally unable to transform the sounds she said and blended together into the word she knew (unless it was a memorized word). Then like a light switch it stopped. She refused all the things she had craved and only wanted me to read to her. About 6-7 months went by like that and then suddenly she picked up a book (easy reader) and read it cover to cover out loud. After that she was back to wanting to read on her own again and progressed quickly. She is a perfectionist and needed submerge the skill until she could do it well.
Another example would be art and to a lesser degree playdough/legos etc. At age 3 I would come to her preschool and she would excitedly tell me she had made me a picture. She would take me to her things and I would find a slightly scribbled upon paper that was cut into tiny pieces. Then she would spend 10 minutes telling me in detail about the picture. There were rare times that she would draw something detailed and nice so I knew the ability was there. I believe she just could not draw the picture she had in her imaginative mind and so she didn't really try.
I agree with encouraging sensory activities. If you have easy access to a good OT evaluation you could do it but it sounds like you could give it some time as well.
