This is so true. Every time I've asked someone in these forums to point to any evidence from FDev on this 10 year plan statement, after they've made this comment, they can't and don't.
This indeed seems to be nothing more than a theory crafted from certain die-hards early last year. Loyal fans who acknowledged the game was in fact very incomplete. I was here starting in early beta and there was never any mention of a 10 year release plan, never. As you suggest, things appear to be getting made up as FDev moves forward; the plan seems to be "what can we do next, and/or what can we do next for $$?". A good example is CQC - sorry, "Arena"- was never mentioned during beta (never mind the change in plans with the name and how it would be sold). xBox and Steam were not going to be supported originally, as stated by FDev themselves, but then this plan was quickly reversed. Planetary landings was supposed to be part of the original release but couldn't be done so it then became an expansion, and this couldn't be achieved so it then became two expansions (lol, maybe it's the 10 year plan itself!). Even the simple CG feature came out of nowhere with no warning and no pre-sell hype after FDev saw players doing group events. Features for Horizons 2.4 are still listed as "TBD" on their website suggesting they can't or won't even commit to things coming this year. And then there's the long list of things FDev said were planned for the game at launch but are still totally missing (NPC wingmen hello? Multiple shields - remember that? Etc., etc...). Strange actions for a company with a 10 year release plan, don't you think?
There's also a lot of 'ADHD' behavior from FDev, that the loyalists shouldn't ignore, which simply supports pessimistic thoughts especially in achieving some sort of long multi-year plan. Things like the Apple app: what's the plan for this now? Has this 'shiny toy' lost it's gloss? Where's Horizon's for Mac players? Elite will lose it's gloss one day and FDev are clearly showing you what to expect.
If there is indeed a 10 year plan by FDev then let's see some facts please, and let's also wish them luck on an ambitious and foolish business plan.