Can someone shed some light on the planned X3C hardware device?
I see no explanation on their website.
Also, where can I find the whitepaper?
Thank you in advance

I would guess at it being some kind of ultra low-powered X3 miner seeing as they plan to bring back mining of X3C in future and with the growing number of Masternodes now active building a solid network infrastructure, what other possible motivation could be behind that decision if it were not financially viable to POW mine?
Just a guess, probably wrong but food for thought of the possibilities.