This subject has been discussed in some other threads, but there are some ideas that haven't been mentioned here yet.
A working moongate home deco. Maybe you can select from a variety of colors, and lock it down in your home. Wouldn't really be overpowered because we already have crystal portals that will take you to any moongate. This will just save you one hop, and you can pop out where you need.
Basement digging tool. I guess this would be a variation on a second home, and would probably be of most interest to owners of classic houses. It would give the benefit of additional space & storage, as well as allowing for a customizable area for owners of old-style fixed housing.
Ethereal mount coloring tool - a little different than the retouching tool which was an 11th year reward (so I guess this would have to be 13th). So, instead of turning your ethy Cu or Hiryu into plain solid color, you can change it to one of the available colors (maybe not blaze or super rare colors). And maybe you can select a different color for the ethy horse and swamp dragon or something. Doesn't have to be too outlandish, and should be super easy to implement.
Multi-school spell books. So, instead of having to carry around multiple spell books if you're a mystic/necro/mage or a chiv/bush/SW (whatever), you can just get one spellbook that holds all your spells. These won't have slayer or any special properties, so you'll still need to carry those separately, but it should save some backpack clutter.
Person bank box. So, you can make and cash in commodities at home already, how about checks? Pretty straight-forward. Make and cash checks at home. I don't think this would be considered unbalanced. It's just I tend to haul stuff home after a hunt, and after a few days I can get quite a few piles of gold.
I'm pretty sure they will add a new mount, and probably a new statue (still looking for a terethan matriach myself). For the mount, I'm going to vote for bouras. I know they probably won't add anything that requires new graphics, but maybe riding a boura can us the same graphics as a swampie? For statue, I'd like a full-size true harrower that talks smack. We got a little tiny false harrower statue, it's time for the real McCoy.