Depends on what Language you intend to code the server in i guess,
Im still toying with the idea of a php backend and a mysql database. using HTTP Post request's Via the client as a connection method.
Might not be the fastest in the world but im sure it could produce intresting results for very small scale mmo's Also makes the entire backend totally portable ( Theres php And MySql Versions for all the major OS's )
And making diffrent client requires no extra backend work ie if ive got a DarkGDK windows based client and a Linux webserver backend, And i want a linux client.
all that would be needed is to recode the client, The server software would never Require changing,
Now try running a DarkGDK app via Linux ( Wine Hates it before thats mentioned. Ive Tried ) Mac Ports would also just be client side.
Also gives the ability to poll the database via a webbased app
( Wow Armoury Style - For those that have never played wow. The website has an "Armoury" section allowing the display of the characters gear exctra exctra. )
Adding that to the server would be a breeze .
Its just a theory im working with and have no code at all to prove it could work, But it's an idea none the less.
Stuck in the land of the confused! and loving it!