Thanks to Flying Wonkey for the Translation
Original Tweet:
It's not a matter of the technology for getting the PS4/XB1/PC players to match up against each other being the issue, but rather first party company policies and potential security risks alongside the community perceived reputation of PC gamers being cheaters that is hindering the decision to allow cross platform play as explained by Tekken project leader Katsuhiro Harada on Twitter to a fan question.
Original Tweet: