I'd be all down with it and all that, but the main problem isn't themes or mechanics or hell even the concept of it being a "FreeRP".
The main problem is player motivation and if it's just going to be a clique-fest, where the people playing are only invested on what happens to their character and they write about just them or their small network of people.
Where you basically get 15 posts of something akin to the Grifterverse where they're posting about their OC non-stop. Now I don't think anyone on the forum is like that per-say, but if nothing is going on or there's no goal to write a story for, then people are going to lose interest and it's going to be really fucking boring.
Look at the Fallen Earth RP where everything was ash, there was no goal and it was free, people went into their cliques did looting twice, ERP happened then it died.
People hang out in their base, they scavenge for loot that literally has no effect on the plot where they don't even bother to have dialogue between characters on looting things or even flesh out their characters, they just go "I loot building and find some food and rope. Then I head back to base.". Then they ask for a dungeon where dice rolling is involved, or people ask for events where mechanics are introduced, that never happens, then it dies.
Hell if you just had two people doing it as a character study it'd be fine. But the question is not "what setting", it should be "what should the goal be?". Is it going to be a study on the group of 2-dimensional characters where only two of them are well-written and fun to read, is it going to tell a story about a power struggle in a group, or is it going to be more about the world and environment and the players are just a vessel to explore something that's written by the community.
You really need to give people a focus or things will get out of hand, people will get bored, and then it dies with the GM or few players that enjoyed it getting salty even though the GM and few players probably posted twice.
Honestly I vote for a medieval fantastical or not and just have it be about two kingdoms beating the everloving dogshit out of each other with the players either being caught in it or feeling the effects of it. Have players be nobles, peasants, kings/queens, or traders that have to deal with the war either losing caravans that are being taken advantage of by bandits or military men or they're making fat profits off the war by supplying weapons to both sides.
Cyberpunk could work if it was going to be something akin to Shadowrun (in plot, not setting) where maybe a corp is getting to powerful in a region and people are working together to take it down.
In short: Just have the kickstart of the freeRP be some kinda goal people are writing to achieve or to flesh out. If you just give a setting and no goal, people are going to lose interest because they'll feel like they're writing nothing. FreeRP without goals can work, but you have to have some really dedicated writers that actually give a shit about it. And to be brutally honest, judging by the state of the Rec Room everything here is very casual and not very focused on creating plots out of nothing unless you're a GM.