Do you think they will expand upon or add a martial arts feature to Sims 4 as they did in Sims 3?

There's still a possibility if they ever bother to explore Asian themes again in the future, but who knows? The Sims 4's future is a complete guess now at this rate.

I think the closest we'll ever get is the sparring from the military career in Strangerville.

I think it'll remain linked to fitness and won't be it's own skill. I always did martial arts in Ts3 it was a really interesting skill but it's been broken up in TS4. The sparring went to the fitness skill and the meditation/teleporting went to the wellness skill.

Martial arts in ts3 is worthy and cool, just like vampire in sims 4, but sadly, I doubt they would do that as because they did kind of add in strangerville, but that is just very simple workout martial, nothing about rank, grow, fighting other sims in martial arts, I do like sims medieval combat, too, fun to watch sword combat, I wish they make Medieval again and this time lot better than old one and add spellcaster and vampire in Medieval, that's would be fun gameplay.

I hope they'll bring back martial arts along with China, Egypt & France.

Same here. I'd love to see it brought back.