It should be possible with a script:
display message using waitingroom (ex: "Hello World ... ")
sleep a short time (250 ms?)
rotate the string 1 character left ("ello World ... H")
delwaitingroom and display the new message, goto #2 and repeat
prontera,155,188,0 script test 910,{
end;
OnInit:
set .message$, "Hello World! ";
while (1) {
set .message$, delchar(.message$+charat(.message$,0),0);
delwaitingroom;
waitingroom .message$, 0;
sleep 200;
}
}