I'm trying hard to make a lot of the suggestions here a reality. I haven't gotten there yet, but I hope to do so eventually. After I feel comfortable with what I've done on my current project, this is what I plan to do:
First imagine every mechanic that Faery Tale Online uses now (*and will eventually have): Real family births and mating, aging effects, multiple races, latitude-based weather + effects, seasons, mining, city building, permadeath, pvp, decay, story logs, *army systems, *farming, *animal husbandry + *mounts, *vehicular and *sea travel.
On top of all that, imagine a browser-based RPG universe with infinite star systems to explore, all generated randomly on-the-fly as player characters come into proximity. Each system would have a variable range of planets, moons and other cosmic entities. Each planet would range in size, weather and ecology with an equal amount of detail as the FTO world. Each description for every plant, animal and natural feature would be spawned from a mega-list of adjectives (colors, shapes, textures, etc). All of this would would be generated at the instant the first explorer comes in contact with a system's inhabitants.
Then imagine that a character or a group of characters can build their own unique spaceships that can be entered, moved about in, and flitted about the universe at varying speeds. Each unique planet and moon can be landed upon where characters can begin exploring, terraforming, and colonizing. All characters will be able to build a huge assortment of equipment beyond the growing list that FTO already has. Creatures would vary wildly in behavior so you could find anything from, docile Ewok-like creatures, to terrifying killing machines similar to the movie, "Alien". There would be no level-scaling here, so exploring new worlds would be extremely risky, yet rewarding.
So that's the basis for my ideal game and future project. The great thing here is that I already have most of the code in place from FTO, and most of the new features planned out. Barring my death, I hope and plan to make this a reality at some point.