The 1080 is great. I think CIG will finally settle on using the GTX 1080 as the gold standard card to run Star Citizen performantly and stop performance creep (meaning, they should stop increasing the specs requirements and target the 1080 to run at high framerates consistently and optimize for that).
Unless of course it doesn't get released until 2020 in which case they might target the next generation of cards... yikes.
I don't think the 980 will cut it unless you're ok with 30 FPS at 1080p60. If you want higher resolution or higher refresh rate, you'll definitely need at least one 1080.