There's actually a lot more Fantasia people in the Marketplace than before. A year or so back (probably even 6+ months ago), for every 15 Jewelia threads there was probably one Fantasia thread if that, which has changed a lot now. I see them a lot more often :3
I agree with you about not putting [J] or [F] in the title though... I've had issues where I wanted an item but the seller didn't include their world in the title and ended up being on Fantasia. >:
As for the population... yeah, it's a lot quieter than before. Though that goes mostly for the whole site. The Trickster section is really the only active section this site has now, I noticed, which is sad.