You don't really expect atmospheric earth-like planets for the next update, do you? If you look at this other WIP space game and consider for how long they work on such features, you can imagine what FDev is going to produce in this rather short time frame with 25% of the staff and also considering the updates we already got.
With that all in mind, I expect we get access to lifeless atmospheric planets, lava worlds (those are already late, right?) and gas giants.
It's difficult to compare other space games becuase the roadmaps are completely different.
FDEV started developing the galaxy and the core game, and that's what they've been doing also for the last 3 years up to Beyond.
Tthen we suppose they will develop legs and atmospheric environments.
Star Citizen did the opposite: there you have legs since 4 years and atmospheric planets since 3. But most of the core game and the "galaxy" are still missing.
Same did No Man's Sky at its first release: legs and all planet types but no contents, which arrived later.
Based on this we should assume that the core features takes longer to be developed than an EVA module and some atmospheric effects (which makes sense to me) so the big part of the job in Elite is already done.
As I already said, Legs and Atmospheric Planets are feasible for end of 2020. One team works at legs and contents for legs and one team works at the graphical engine to add atmospheric planet. I'm not saying we will have water worlds with giant whales and ELW filled with life though.
I guess we might see Ammonia Worlds with Thargoid bases, generic planets with clouds (rocky/ice/HMC).
If we're lucky we will also get Volcanic Planets and Gas Giants (but I doubt). ELW and WW will come definitely later when FDEV got also vegetation and life developed.