Don't you want to see the home of the dragonlords?
HBO is currently working on several Game of Thrones spinoffs, and I would like to put forth this suggestion -- a show focused on the rise and fall of the Valyrian Freehold. Who doesn't want to learn more about the people we have been hearing about since the early days of Game of Thrones? Also, the story of Valyria has plenty of connections to the much, much later story of one Daenerys Targaryen.
Quick history note: As the western world recovered from The Long Night (remember Old Nan's story to Bran Stark in the first season of Game of Thrones?), empires rose and fell in the east. The first known empire was Old Ghis, whose power was built upon slavery. Amidst the great volcanic mountains called the Fourteen Flames, Valyrians, known for their great beauty, learned how to control dragons. The Valyrians called themselves a Freehold because all Valyrian citizens that held land had a voice. Old Ghis and Valyria fought five great wars, all of which the Valyrians won with their dragons. On the fifth and final war, the Valyrians completely annihilated Old Ghis. Their dragons destroyed Old Ghis's pyramids, temples, and homes. The Ghiscari who survived were enslaved; as the ages marched on, they even forgot their native tongue and only spoke High Valyrian. Following the Doom of Valyria, the Ghiscari re-established their slave trade; Game of Thrones fans would be familiar with the cities of Astapor, Yunkai, and Meereen, all cities that Daenerys Targaryen conquered on her way home to Westeros.
As Valyria expanded, many fled the reach of their empire. Braavos was founded by slaves who escaped Freehold, but the other Free Cities maintained their ties to Valyria. Many notable Game of Thrones characters came from the Free Cities, including Arya Stark's dancing master Syrio Forel (Braavos), Jaqen H'ghar (Lorath), Varys (Lys), Thoros (Myr), Area Hotah (Norvos), Illyrio Mopatis (Pentos), Vargo Hoat (Qohor), Daario Naharis (Tyrosh), and Talisa Maegyr Stark (a show-only character, but she's from Volantis).
The Andals of Andalos lived in prosperity for a few centuries, but with the fall of Old Ghis and the rise of the Valyrian Freehold, they, too, had to flee to avoid slavery. The Andals first landed in the Fingers (Petyr Baelish's home) in the Vale of Arryn. After the Vale was secured and the Arryn kings had supplanted the High Kings of House Royce (descendants of the First Men), the Andals proceeded to conquer the rest of Westeros. The worship of the Seven Gods that we see in Game of Thrones was brought to Westeros by the Andals. Only the North successfully managed to repel the advance of the Andals and continued with the old ways. The clans of the Mountains of the Moon (Tyrion's first army in Game of Thrones) were descendants of the First Men who did not bow to the Andal invaders. The wildlings north of the wall are also descendants of the First Men, as were the Starks of Winterfell.
The people of the Rhoyne were initially accepting of Valyrian outposts along Mother Rhoyne, the mightiest river in the world and home to great Rhoynar cities. As the Valyrian towns grew into cities, however, conflict rose, and eventually, wars. The Rhoynar princes led by Prince Garin banded their armies together to fight the Valyrians; only Princess Nymeria of Ny Sar spoke against this plan. The Rhoynar did initially experience some success (they brought down two dragons and injured one), but when the Valyrians came with their three hundred or more dragons, Prince Garin's army was so thoroughly defeated. Princess Nymeria gathered what was left of her people (mostly women, children, and the elderly), placed them in ships, and sailed for years until they found a new home in Dorne. Mors Martell, then the Lord of the Sandship, married Princess Nymeria. The Dornish tradition of calling their ruler 'Prince' or 'Princess', and of equal treatment of men and women (if the first born is a woman, she is the heir, even if she has a younger brother), came from the Rhoynar. Arya Stark named her direwolf Nymeria.
As Valyria strengthened the grip of its empire, it also built its westernmost outpost -- Dragonstone -- two hundred years before the Doom and Aenar Targaryen's flight along with his family, his slaves, and his dragons. Dragonstone would later be known as the ancestral seat of House Targaryen and, later, the ancient castle under the command of Lord Stannis Baratheon, brother and true heir of King Robert Baratheon.
There is so much story here, and they are tied to the events in Game of Thrones so that even show-only viewers can readily follow the events. I am currently so thoroughly enjoying House of the Dragon, and very hopeful that these stories of Valyria will make it to screen at some point in the future.