I think Star Citizen will never be finished. Meaning that eventually the game will "launch" but be managed as a GaaS title / MMO. They'll continually add new ships to the game, sold in this pretty disgusting way, targeting whales to fund the production of more and more planets. The game will continually expand until people stop playing. I think it's less disgusting than loot boxes though. These ships do get added to the game, or people would stop buying them (the 890 Jump was added very recently - a previous big money ship).
I think Squadron 42 (the single player game, kept mostly under wraps like any traditional game dev process) will release 2020 or 2021 though, for PC and next gen consoles. That's the point we'll see fully polished gameplay systems, which are always late in game dev anyway. I imagine Star Citizen will enter some kind of release state on PC and next gen consoles within a year after that.
No idea on the % of ships available, but they're added regularly enough. 890 Jump being the most recent. Gameplay systems have been trickling in too the past year or so, with bounty hunting, mining, mission running, trading, smuggling, piracy, exploration of planets etc available. All still need futher polish, and many will obviously benefit once new planets and systems are added. It's got a long way to go, but with SQ42 still a good year or two out, the systems side really isn't look so bad. I think the main thing Star Citizen needs to push all these gameplay systems is more planets and systems to push the space-sim sandbox potential. Most of that focus is understandably on SQ42 right now though, but presumably all planets made for that game will also be pushed into Star Citizen, and then the team focuses entirely on content for Star Citizen.
