The functional differences between using the PTHD and Dante expansion cards are minimal. The PTHD card has a few configuration options in the H9k’s settings, while the Dante card does not have any settings on the H9k itself and all setup is done in Audinate’s Dante settings. Beyond that, there is no difference when you are routing your effects and I/O using Emote.
Latency information for each can be found here:
As you said, Dante networking could provide you with more flexibility for future expansion.
Let me know if you have any other questions.