I love the historical and fantasy but I'm definitely running out of good ones to watch.  If you look at my list I've seen quite a few and I'm going through withdrawal. I keep hoping for Gu Family Book 2 to no avail.  PLEASE someone recommend something worth watching. I mainly watch K dramas as they are USUALLY of a higher quality than others but I'm willing to watch GREAT drama no matter what country it's from.  I also like happy endings... I know that that eliminates a lot of dramas but life is hard as it is... I watch to feel hopeful... not depressed. LOL! I LOVED Jewel in the Palace, My Girlfriend is a Gumiho, Rooftop Prince.... So many... but if you can recommend one that isn't on my list, please do.  Thanks and happy watching!

I'm surprised you don't have Empress Ki in your list  it's high quality, Korean, and just a sageuk (historical) that is REALLY well done  <3

i recommend that you try it next  
I didn't see it on your list so my recommendation is misaeng/incomplete life. some people drop it because of the bleak atmosphere that misaeng starts with, but it's a wonderful journey to go on with jang geu rae & it has one of the most satisfying, uplifting endings. it's an exceptionally well-made drama in all aspects, imo, & it left me feeling so, so happy (but also sad because it was over).
Jdrama:
Buzzer Beat
Maou
Pride

Kdrama:
The moon that embraces the sun
Based on your preference with fantasy and romance I recommend these:

Big
Blood
I love Lee Tae Ri
Lie to Me (not fantasy but one of my favorite romance dramas)
Splash Splash love
Night watchman's journal (couple first episodes might be a bit boring because it's kinda doing the background for a story. But rest is great and I think the feeling of this is close to Gu family book)

And couple chinese dramas that I love (fantasy element is great in these)
Love through millennium (remake of Queen In Hyun's man)
The four (2015)
Korean:

Arang and the Magistrate
Warrior Baek Dong Soo
Faith


Japanese:

Tempest
Jin

Chinese:

Scarlet Heart
If you loved jewel in the palace, you will like dong yi and empress ki. Both of them have intelligent woman character and great story. You can try Chinese dramas like Prince of Lanling and Journey of flower!!!
I think you should try Six Flying Dragon , its really good 
Yi San
Six Flying Dragon followed by Tree with Deep Roots
Try Ballad of Seo Dong

If you don't mind Chinese, my fav is Nirvana In Fire. Well made and veryyyyy addictive. I was going crazy waiting for each episode back then. It's not a romance drama, though.

Chinese: Sound of The Desert. I swear the male lead in this won best imaginary lover award in all of dramaland.

Another Chinese with happy ending: Legend of Lu Zhen (on your plan to watch list?)