Two thoughts come in mind about network access and latency.
First, the keyboard must have "full access" to be able to make network requests, which is a setting that the user must switch on their own. I'm not 100% sure what attitude app assessment takes on this, but they can not appreciate a keyboard that does not have functionality even unless the user gives full access. Consider having some kind of barbone offline mode, if possible with your usage case.
Secondly, network delay will really be a problem if you expect people to write on this keyboard at noticeable speed. The delay between a user who writes the last word of a word and those touching the space bar can be small, can you round a full request and process the results in less than that time?