Mysterious superintelligent AIs, which are too smart to communicate with baseline humans. I think this is just a plot device for post singular fiction. You just

Mysterious superintelligent AIs, which are too smart to communicate with baseline humans. I think this is just a plot device for post singular fiction. You just can't write superAI explaining its own behavior, because you aren't smart enough. The best you can do is write about mysterious AI, which can't communicate with you or can't explain its own actions because they are too complex to explain. Returning to your post, I think that human-AI hybrids will be perfectly able to communicate or explain their plans to baseline humans (merging with AI should enhance communication capabilities, not hamper them). They could have problems explaining their feelings, thought processes, perceptions, as those things may not correspond to anything baseline human experiences. They could have no reasons to talk to baseline humans at all. But it is not inability to communicate.