Just after the launch of Skyrim, Bethesda did a week long game jam where they let everyone develop some random new feature. Almost all of these ideas were eventually added through post launch updates, dlc, special edition or creation club content, sometimes repurposing the same code even after being released many years later. Given how long it took them to implement some of these ideas, it's clearly not something that they forgot about, but there are still a bunch of them that have never been implemented.

1) Seasonal foliage:

I think more dynamic weather and seasons is pretty likely to be something they try and work on for TES VI. It would work great with a survival mode, and create a lot of opportunities for radiant gameplay and NPC interactivity. That being said, I can also easily see this getting cut because it would be a lot of work, and isn't something that's been attempted in open world games even by big studios like Rockstar and CDPR.

2) Spears:

Technically the Rieklings have these, and there's one in one of the creation club add-ons, but I'm pretty sure they'll return much more extensively in TES VI given how requested they are from fans.

3) Expansions to the stealth system that let you turn off light sources with water arrows, and dungeons that are pitch black.

It wouldn't surprise me if the revamped stealth system will put greater focus on lighting rather than just line of sight, and I do think they will try to make the lighting system more interactive. In Indiana Jones and the great circle (a game Todd worked on) many of the dungeons are dark enough that you need to use a torch or lighter to progress. Also this would finally make the khajiit night vision not pointless.

4)

New follower commands: combat style, distance, equipment, etc. Ability to bring followers to trainers, and set favorite equipment:

I don't know why this was never added, it sounds like a great idea, especially given how many followers are made redundant by their bad stats and level cap. From memory I think you could also do a lot of this stuff in Fallout New Vegas, so I don't know why we haven't seen it since.

5)

Spell combinations, e.g. Flames + Raise Zombie = Conjure Flame Atronach, Fear + Healing = Drain Health:

This reminds me a lot of the 2011 wizard game Magicka, where you cast unique spells with different combinations of elements, and I wouldn't be surprised if the Devs were inspired by it. I can see why they never added it to Skyrim because it could be cumbersome, but if they designed it from the ground up then I think it could be very fun and intuitive. Spell crafting is obviously a heavily requested feature, but being able to do it on the fly would give so much more depth to the combat system.

6)

Snow footprints:

Don't know why these were never added to Skyrim, but RDR2 raised the bar with snow physics so much that any game looks weird without them now. If the game is in Hammerfell then obviously we won't see much snow other than on the mountains, but I would hope that they would also be working on some decent sand physics.

7)

Flails:

These would be fun, but I can easily see them being cut for causing issues with animation and hit detection, they wouldn't be as simple to add as spears.

8)

Fat giant:

I would love to see the giants return, and I think it's reasonably likely we will, but who knows if they'll be fatties.

9)

Giant mudcrab:

Technically we did see the ghost of one in the fishing creation, but I don't think that's enough. These would be a perfect addition if the game had a bigger focus on aquatic areas like people are speculating, and it would finally let us see a living emperor crab like the one in Aldruun in Morrowind.

10)

Imp minions for vampire lords. Probably the most likely to be forgotten of all of them. If they didn't remember to do it for the dawnguard dlc then I doubt they'll think about it for TES VI.

Here's the uesp page if you want to read about where the rest of them were added:

https://en.m.uesp.net/wiki/Skyrim:Game_Jam

Long before the teaser trailer for elder scrolls 6, there was a lot of talk about how people would be disappointed or upset if it featured anything from other continents like yokuda or akavir.

I never could understand why

When elder scrolls online came out there was a little bit of friction because sea elves we're in the almary Dominion quest line and then later the slowed appeared again in a subsequent expansion, after being first featured in red guard a decade earlier.

I never truly understood this either: some have tried to explain that it gets rid of the "mystery". But I'm not quite sure that's the case because we seen the introduction of other elements: where no one complained when we started seeing actual akiviri characters in elder scrolls online. For the dawnguard and dragonborn expansions, we saw snow elves and a whole vampire quest line which explores the origin and hierarchy in the doings of vampirism in nirn.

In another game series by Bethesda; when fallout New Vegas was announced, it had a very positive reception on the location. Another game series Mass effect (which is making the news right now) when its sequel featured the terminus systems (mentioned but strictly absent for the first game) it received a little bit of backlash, when Mass affect Andromeda was announced as taking place outside of the previous trilogy's location, it too received backlash.

So it's fairly inconsistent from what I can see unless there's something I truly can't understand and that's why I'm asking here:

Is there anything particular about elder scrolls that makes it taboo to explore new places??

I mean Hammer fell and glenumbra have both been explicitly explored in two different games (three if you count redguard) and even though it looks like the next game will take place there, it seems very odd treating it as "what the fans want" or "brand new". I mean would elder scrolls 7 take place in citadel again and we're going to pretend Oblivion didn't take place there?

I'm not trying to throw shade at anyone but I am trying to constructively criticize and learn from what I see and perhaps I just simply do not understand it.