It probably was possible years ago. But they decided to do other stuff first. If they had done walking in ships then other things would have been pushed back.
Sure, we can argue what FD could have dropped or pushed back. Powerplay for example (hehe, i've summoned Rubbernuke) but its not like devs can magically just do stuff without assigning time and resources.
Everything comes at a cost.
How many decades was it since FD announced ED to when it was released?
Announced as Elite 4 in the early 90's and then shelved by FD until early 2000 at least.
Finally released in 2014 as an online only game that a lot of people were severely disappointed about.
That's 24 years of potential development time, at least half of it wasted while DB waited for tech to catch up to do what he wanted. They could have assigned a small team of 3 to work on it during that time to do most of the things like this. It's not like it had never been done before, the original Freelancer from the 80's went to different places in the station, even though it was teleport to each location. WOW and many other similar games allowed walking seamlessly around a huge map. No, instead, Elite 4 sat on a shelf gathering dust for most of those 24 years.
IF DB was serious about producing a mind blowing game when tech allowed it, he would have worked on it, even on a small scale, to get it ready. Instead he sat on it, doing nothing until over 10 years later. When it did hit the market, even Star Citizen was doing stuff like walking in ships and on the landing pads that ED should already have been able to do.
A little back history:
After a lengthy legal battle to wrest the rights to Elite from Ian Bell, DB then announced Elite 4 under the name of Frontier Developments.
This announcement was shortly revoked and the web site taken down, much to the disappointment of many fans while DB said he "wanted tech to catch up with his vision of the game."
Frontier Developments went back to creating quick and simple games, many being developed for mobile gaming industry.
Any contact with Frontier about Elite 4 were met with silence.
Many fans speculated that the original announcement was DB flexing his muscles to tell Ian Bell that he wasn't needed to make the game, but DB grossly overestimated his own skills, realising that he wasn't actually skilled enough to do it on his own after all. He needed more skilled programmers etc to help. When I read that speculation, I did see the logic in how people had come to that conclusion.
This speculation by fans was supported by the release of other online games with a persistent map (Eve Online in particular) and detailed graphics that had been in heavy early development during the time DB shelved Elite 4.
Fast forward a little under 10 years and FD suddenly announced Elite Dangerous. A lot of fans were a bit jaded from the previous false announcement.
What was finally released was similar to Eve Online with a cockpit view and minus the jump gates, but still warping in to a set location. No ability to get out at a station (even though Eve Online had already cracked that with WIS, albeit with a black screen transition and SC had already developed walking around seamlessly from ship to station).