I still can't seam to understand very well, do you also get 50% of something else apart from keeping your NXT and getting 1:1 ARDR?
Yes, there is also tokens called FNX, these are the first child-chain that Ardor will have. The distribution of the FNX Token will be based on each accounts NXT holdings at the time of the Nxt 2.0 Genesis block creation (somewhere Q3 next year).
You can find details here:
https://nxtforum.org/core-development-announcements/announcing-nxt-2-0-roadmap/