SE will never do it unless it's absolutely necessary.
I'm curious what is "absolutely necessary" in their POV, I mean there are several servers that is pretty low pop. Might be a timezone issue but I recall when I took a trip to Siren (IIRC) and my old endgame server of Ragnarok, and both barely cracked 300 people online during EU peak-hours.
But, If I'm being completely honest I think it's fine as is. They run a discount campaign at least twice a year at this point (when most people take a shopping trip to Asura) it's pretty trivial.
I saw someone suggested joint AH system between the servers, the IT person in me just cringe at the idea, I can't imagine that ever happen with the limitations they already experience, that should probably happened over a decade ago when they made the AH combined from all the cities.
At this point after playing for around 20 years, I probably been on all servers at some point (where Bismarck, Shiva, Odin, Ragnarok and Cerberus been where I spent most of my days in the 75-abyssea era at), in 2025 I think Bahamut and Odin hit the sweet spot on feeling like an active server, nowhere near the culture that Asura experience, no real RMT yells outside of ML/JP and practically no mercs.
If people aren't willing to pay $18 to transfer
Eiryl is right. I have seen some players paid to transfer to Asura just to buy stuff from the AH then paid again back to their servers. That's silly.
I don't think it's necessarily silly. People might want to take "advantage" of the generally lower prices on Asura, and supply on certain items but are not interested in all the other things that Asura are known for.