In a way the enormity of making single player as rich as online multi which emulates as near as dammit the Milky way was obvious from the start if you think about it with a handful of DVD-ROMs, and would eventually be beyond the scope of a PC because it would outgrow your hard drive eventually wiiith ny new DLC/updates/patches when you DID manage to update it now and again. And even so, you could make the entire single player install - oh I dunno- 20GB in size, but it would always be stuck in aspic, AND conflict with the cloud/server side galaxies' events. It would be like running two parallel universes/galaxies
You are talking about technical issues that I am guessing you don't have a lot of experience with, (correct me if I am wrong).
The real point to be made here is that an offline mode is not impossible to achieve, not even close; it's a series of technical hurdles, balancing tradeoffs and resource/finance allocations dependent on how accurate and faithful FD want the offline experience to be compared to the online experience.
How do I know this, well it's what I do for a living, but much more importantly the FD developers apparently believed exactly the same thing up until a short time ago, hence the bomb drop a few weeks before release.