Atlus released a few new videos detailing Soul Hackers 3DS's new features, and paramount among them is SPEED. The game now runs at a pace like a racehorse shooting out of the gates, opposed to the original version's feeling of wading through molasses. Of course, the other obvious new feature is the voice acting, which doesn't excite me either way (except for how they treat the demon-speak...and REDMAN), but it's there.
Honestly though, it doesn't look like a huge effort was put towards modernizing the game further than the increased speed and use of the second 3DS screen for a constant map. However, both of those are kind of huge in making this game appeal to the modern SMT fanbase. Keep your expectations in check for a game that's similar to Strange Journey, albeit with fewer features.