Fallout 4 character development is essentially similar to Witcher - you just level up and open new perks, find better gear, etc.
And yes, I don't like it in Witcher and I didn't even play Fallout 4.
On the other hand, there is a lot of things that TES VI can borrow from Witcher.
1. Quests and story writing. I don't get your point about two different types of games. Witcher 3 is a huge open world. Sure, it's not very similar to Beth's open world, but still. And it easily includes well-written quests and main story and open world simultaneously.
2. Crafting. My god, crafting in Witcher is the best which I have seen. Tons of reagents, materials, different ways to craft a special item... Every RPG in fantasy setting should borrow it from Witcher.
3. Leveled areas. TES is all about freedom, blablabla, but if this freedom includes going to deepest dungeon and see only rats there on level 1 (and a diseased rat as a dungeon boss)... well, you get Oblivion's auto-level.
4. Social problems, politics, racial prejudices, religion... I hope that Witcher's success will show Bethesda that you don't really need to make a sterile game which tries its best not to offend any other person in the world. Witcher has a gay character in the starting location, who is expelled from community for being gay and whose story is essentially an enormous part of White Orchard's troubles. And it's not about bashing homosixual persons - it's about how they were seen in the pseudo-medieval society. It seems very strange and immersion-breaking to me, that every nord in Skyrim with whom I fought enemies, says that feels something special to me when I put on the Amulet of Mara. Racial conflict is more or less believeable, as well as religion problem with Talos. But Bethesda surely can't be brave enough to center the whole plot around bringing down false gods like they did in Morrowind...
5. Mini-games, at last. It's ridiculous that there are none still.
Generally, I want to see a more controversial and mature game which isn't trying to be loved by anybody. You take higher risks, you get higher rewards.
Spoiler: none of things mentioned in my post will actually be present in TES VI. Why? Because Beth will sell 20 millions of copies without even trying to be less sterile. And I will play it too in the end.
More spoiler: well, mini-games can surely be included. They do not offend vocal minorities, after all. Although a player can lose a mini-game and become upset with Beth