Geographical overhaul. Making the world feel more like an actual world instead of an infinite grid by showing the player (or at least the option to see) the generated world map like Dwarf Fortress does. Maybe even mark some points of interest like NPC cities and dangerous locations (goblin town, necromancer tower equivalents). I've always been more eager to travel thousands of blocks when I knew I had a destination. Randomly wandering in hopes of finding something isn't as appealing imo. Seasons, climactic bands and weather (possibly with cold/heat effects on the player) should be present.
NPC states, cultures etc. A deep and organic NPC presence in the world can be a key selling point and can multiply the replay value of the game. The possibility to be a part of an NPC community (perhaps even manage NPCs) could be a funner and more organic alternative to solitude and automation. Trade should be important, but it should lay on a bed of economic dynamic (like the kinds of commodities produced in each village/city, the demand for others, etc). NPCs can extend play by (potentially) hundreds of hours, and depth in NPC cultures and dynamics offer a reason for the player to want to play again once he/she gets bored with the current world. I hate to bring up DF again, but I personally know people that have been playing one world for years and thousands of hours, and are continuing to this day because of the depth of NPC cultures and dynamics.
Armor smithing, Cloth and Leather work, Cooking (more immersive), Brewing (potions and alcohols) and Animal husbandry (look into Animania). Horses!
Above are what I believe are must-haves that will make or break it. The following are things that I would personally like to see before the game leaves early release:
Ships and carts (not just boats or mine-carts). These would make trading complete. VS has limited character inventory space, it would only make sense to allow these methods of transporting goods and players. VS also encourages the player to set up mines in different locations, and carts/ships would just make the travel between mines more immersive and convenient. It think if done right, full sized ship mechanics would REALLY set VS apart from other voxel games, especially if paired with immersive NPC economics. If ships are a thing, perhaps a crew could be too.
Random lore. I really hate the idea of having premade lore in VS. I think this game should put no chips in a pre-made story. I strongly suggest that lore be generated with each world, instead of trying to come up with a single setting. A story written by the authors of the game will fizzle out after a while, and serve as no more than an obstacle for those who want to deviate in their own server setting. However, lore generated uniquely for each new world ensures that the sense of mystery and the wish for discovery never cease to be present. Creating lore algorithms may be a bit of a challenge, but it's possible and it leaves us with a system that can leave all the focus on developing game mechanics.
Character customization. I think Seraphs are an interesting idea, but I strongly believe that allowing players to be humans will be a simple change that will appease MANY people. I personally like to be something familiar; having an alter-ego that someone personally created can only enhance the experience.
Jewel crafting, strategic/economic metagame, player managed NPCs that replace automation (mentioned briefly above), mythological creatures and deeper combat are some of the things I think would make the game feel truly complete.