Information from Star Wars Celebration in Chicago. Looks like there is a new expansion coming but it won't happen till September 2019.
FREE expansion for subscribing for one month.
SWTOR: Onslaught
NEW story line
2 new planets: Onderon & Mek-Sha
5 new levels (Now level to 75) - One new max level skill for each spec.
NEW Flashpoint - on Corellia
NEW Operation - on Dxun (new area/planet maybe)
NEW gearing system - Major renovations to gearing and gear.
NEW tactical gear slot to help specialize you into how you want to play your toon. Hopes to add flexibility.
NEW set bonuses
NEW Non-combat bonuses (Unsure exactly what that is yet)
NEW ways to help legacy system be more friendly.
NEW race: Playable Nautolan
No word on PVP at this time
http://www.swtor.com/info/news/article/20190413