I tood delivery of my Model 3 two months ago with FSD purchased, and considered it partially a goodwill donation to the cause, and partially a way to keep Tesla's feet to the fire to eventually deliver the functionality. (If no one purchased it, Tesla wouldn't feel much obligation to deliver it.) They do NOT want to be in a situation where they have to refund tens of thousands of customers; I'm surprised Tesla offered FSD at all to leaseholders, given the near-zero chance that FSD would be meaningfully available in a 3-year time frame. (I intend to keep my car for eight years or so, and I do think Level 4 FSD is realistic within that time frame, which was part of my decision.)
OTOH, I will be flabbergasted if Level 4 FSD is available by 2020, though I do expect to see some differentiation between "FSD" and non-FSD packages before then. For instance, we could see onramp-to-offramp FSD (Level 3 autonomy) as part of the "FSD" package, but not as part of standard Autopilot. I would expect this by 2019-2020. Surface-street FSD (in whitelisted areas and good conditions) will probably not be ready til 2021-2022, and Level 4 FSD in the general case (excluding extreme weather or very difficult roads/conditions) probably won't be ready til 2023-2025, and almost certainly will require substantial hardware advances to AP2: faster computers, more cameras and/or radar, possibly lidar.
I actually nearly held off buying my Model 3 to wait for"AP3", but I'm pretty sure the federal tax rebates will be gone by then, and also I think pre-buyers of AP2 FSD will likely inherit these upgrades for free (or at the very least be refunded the $3k) if AP2 proves insufficient to the task. I still own my "vintage" 2012 Model S, which drives (er, is driven) like a charm, and plan to upgrade it to a new S or X once "AP3" materializes, or once FSD is meaningfully enabled.
Tangentially I've also wondered whether an ulterior motive of SpaceX's proposed global internet constellation is to provide reliable real-time communications specifically to bolster Tesla's FSD systems. There could be some real synergy there.