Depends on what you mean by lead up.

The story is the furthest along chronologically, dealing directly with the events that come after Sora gets the letter in the epilogue of KH2. Whether or not KH3 will take place immediately after this or if there will be another game (chronologically) is still to be seen.
All Nomura has said on it is that there will definitely be a secret movie pointing to the future of the series, as well as that the game will contain answers to those looking forward to KH3. That's obviously pretty vague though, as he could simply be referring to the overarching story that KH3 will deal with(we already know the jist of that though)
It's also worth noting that the Final Mix of BBS's secret movie pointed to the possibility of a BBS: Volume 2, which will certainly have a big impact on KH3's story if it's made.