LaveCon 2015:
https://forums.frontier.co.uk/threads/lavecon-news.165775/post-2529743
July 2017:
https://www.reddit.com/r/EliteDangerous/comments/6orb20 Source: https://www.reddit.com/r/EliteDangerous/comments/6orb20/david_braben_hopes_elite_dangerous_keeps_going/
https://wccftech.com/braben-elite-dangerous-going-10-years/
The second is what I mentioned. Saying "I hope ED still exists ten years from now" really doesnt count as a plan. The first you mentioned is of a forum user saying someone else at some point said there is a plan, without any additional info about who said it, or what he means with a plan. Sorry, that doesn't count either. I can quote dozens of forum members claiming there is a plan, but none of them matter.
So, again: can anyone point to anyone from FD saying they have a legit plan spanning ten years? Not someone saying they heard someone else say something about a plan, not someone saying he hopes the game still exists in one form or another in ten years, but an actual plan.