I know I'm not the first person to suggest anything even remotely close to this, but I feel like now that we have a text-interactive item type like message books, the least we could have is something like a memorial stone that would allow a player to put a small amount of text in to honor someone or something in a more direct and personal way.
I also say a memorial "stone" just because it's probably the easiest means of having something like a grave marker, but also something that could be used indoors if it was made as an indoor item as well. It might not be something ornate or fancy like a statue or something along those lines, but just a rock with maybe some visualized writing on it would allow for the most minimal design required. Heck, there could even be some kind of story factor involved (like a beast tribe element) to explain why it is what it is.
A lot of us players have lost someone who we either met through the game or played the game with. I believe that having a simple item like a memorial stone would be a great way of not only allowing us to honor their memory, but also to allow others to see why we do so and hopefully honor them as well.