lower the sub to 10$ instead of 15
release new models with the next expansion
feature old time favorites like alleria, turalyon.
add a class or race with high fanbase instal like naga, ogres, ethereal, or demon hunters
merge a few of the lower population servers
make level cap 100 so they can use it in marketing campaigns to go along with the 10 year anniversary
have big marketing campaign like in wrath and bc with all the celebs.
i think all of this would see a large influx of subscribers