Most producers letters these days are glorified forum posts. 3-4 short paragraphs. And really, that would be enough, no need even for any pictures. Just a short rundown of what is planned. That takes 1h to finish, and that is extremely generous.
Not having a producers letter by now tells me they dont care or they dont know what they will do after 4.1. Right now i guess all members of the team are working on 4.1 full time. No thoughts about anything else. After release there will be several weeks of furious patching if i look at RIFT history.
After that they will probably take a hard look at the general state of the game and then decide what they want/can do in the future. I guess big things are no longer feasible. Maybe then we will get a letter