Forgo Character Sheets, do applications via 'Introduction Post', so to apply, you have to create what would be your character's first post. Obviously, the GM IC launch will have to be live at the time of applying, but this would alleviate the first post dilemma where if you can't come up with a first post, you simply can't apply. Character sheets are easy to write; posts are a bit harder. You would be free to deviate or expand upon your first post so long as you do so within the applicable window. If at the end of the window, you have not posted the 'post' that you submitted for application, you either have to post it or withdraw.

Take the linear sandbox concept, but make it fantasy instead of Superhero.
Allow Player development, but certain concepts be unified (magic, for instance, needs to function universally)

The basic premise is that players are sent into the 'badlands' to hunt and defeat some sort of creature or corruption. Elements of quest, but also discovery and combat, rival factions, player versus player etc.

The Badlands, or Neutral Zone, would be territory inhospitable to the surrounding nations, preventing expansion, but also home to enchanted forests, harsh terrain and creatures which are nigh unkillable.

Players would need to portray mercenaries, hunters etc. No character sheet, instead players would apply with an opening post. As the game would be run by posts instead of a character sheet, accepted players would be asked to produce a list of relevant names and a quick paragraph describing their character and their relevance within their plots and stories. Faceclaims would be completely option and the focus more on storytelling, text and ideally collaboration with opportunities for both large-scale group adventures and smaller dynamics.

Dark Knights of Steel Inspired

Tattoos from bio-luminescent flora that's near invisible in the daylight but at night give the island people a rather eerie appearance.

Technology, time frame level, roughly equivalent to real world 1650s to 1730s, think Musketeers, Golden Age of Piracy, at least one of the nations inspired by a more Frontier time period.

Inspirations of Dark Knights of Steel, Avatar the Last Airbender, Lord of the Rings, Pirates of the Carribean, Zorro and Robin Hood.

Death to Tyrants. False King on a stolen throne leans on the word of a seer who earns of a deadly fate.

Rapiers, bucklers, wheelocks, flintlocks and at least one nation having access to early caplocks. Bows would still be prominent, with crossbows also available. Other melee weapons would still hold up with the longsword remaining unmatched as an option along with arming swords, hanging swords etc.

Combat and its weapon choice would be at least in part be circumstantially influenced.

Three(?) creator deities, [Alternatively, a triune deity whose different aspects have gone on to be worshipped as their own individuals across various nations], this (one) celestial being would then lead to polytheistic and monotheistic religions with overlapping parallels and traits all pointing back to the truth of one actual divine being.

Magic was birthed from the residual primordial energies used to create the world. To some, magic is almost another deity, thought to be a living force that entwines every creature and man across the globe. Some cultures worship magic, and those touched by its gift are exalted to higher positions in society. Magic flows through all of nature and every living being.

In the same way that anyone can learn to sing, anyone can hear the call of magic, but not everyone will have the same talent for it. Some magical abilities are accessible to everyone if they hone and practice listening to the flow and call of magic, abilities such as pushing objects with one's mind, summoning a ball of light in the dark or pushing a leap even higher. But, among the population of every nation are those who are called the Faeborn, individuals who have unique abilities or gifts linked intrinsically to magic. These traits and talents vary widely from one individual to the next. While many are invisible, there are many more that are very visible, causing physical disfiguration or taking on a monstrous appearance. Some talents seem to occur more frequently within specific races, while others are so destructive that these Faeborn are immediately hunted down and destroyed at the first display of their abilities.