That's realistic? I'd say optimistic.
I think we're looking at a situation similar to stations. You'll drop into atmosphere (accompanied by a brief loading screen similar to that when you drop out of supercruise at a station), into an instance with a terrain about 300km in diameter, with a station or other point of interest at the center. There will be maybe 15 or 20 terrains, with maybe 30 or so different overlays to make them seem different.
That's what I think we can expect, given what we've seen so far and given the size and resources of Frontier, and that's no bad thing.
Do you really think FD were that stupid to do that? They'd get ripped apart both by the playerbase and the press, especially in the face of No Man's Sky (regardless of that game's unrealistic scale, the fact they do seamless transitions at all means that
everyone, myself included, will expect and accept no less in ED).
I honestly think FD can pull this off, and that they already have a plan how to do it, possibly even started working on it. David Braben himself has given us some hints even, when he said planetary landing would begin with airless moons. Because that it precisely the simplest type of planetary landscape to generate, and from that they can build up towards ever-increasing complexity, next step would be atmospheres, with surface ice, clouds, surface liquids and weather, after that vegetation, then animals, and civilization could be done in parallel to these developments, beginning with small surface outposts, growing to the equivalent of starports (e.g. a domed lunar city), until expanding to open cities connected by procedural roads, railways etc.
Considering that by the time they are at the point to do animals, or open cities, it may very well be 2017 (assuming landing on airless moons comes in 2016), tech will have advanced and handling that much data becomes more feasible than right now.
I would not be surprised if FD could produce planetary surfaces already with the terrain detail required for landing on airless moons just by cranking up some value that says "only create detail down to this level of precision", and just the servers and/or clients couldn't yet cope with it in real-time (be it due to lack of optimization or hardware capabilities).