I am not planning to build any web site soon but I can give you and idea of what is coming.
Library Science: I am a library and computer technician and I think that library science should have a more important place on the internet. Library science is not really vulgarized compared to computer science. You will not find a book called "Become a librarian in 21 days".
So my objective is to make a website where I will explain how library science works. So that the common people understand how it work which might increase it's application in everyday life. The second objective is to remind people who work into libraries how and why it works like this in many working environments, some rules and concepts seem to be ignored and forgotten.
One of the problem I have with this website is that I might make it a bilingual website (English-French). This means that it doubles the amount of work I need to do.
Thematic Index: I am not really sure of the name yet because there is nothing close that exists yet. This will be a site mainly for people that create things, especially games. I'll explain the purpose with an example.
Let way you design a video game and you want the player to be able to research technology. So you need a list of technology for your game. Where is the first thing you will look for inspiration? Most people will take a look at the civilization games because it is a very good start. If you were making a sci-fi game, I would have suggested master of orion 2.
Now the problem is that even if these games are a good reference, they are not necessarily complete. So my idea was to combine various information from many games together to have a more complete reference. So if I take a dozen of games that has a tech tree and combine all their technology list, the result will give a more complete list of technologies.
So my objective is to take games and extract all keywords and information that could be a source of inspiration. Classify these keywords according to their subject and create a large thesaurus or index of words. Then people could browse a certain part of the index for inspiration. There is no definitions like a dictionary, they will only be list of keyword that you could browse.
The problems in developing this website is that I will need an SQL database, and I might need to code some stuff. Pmwiki seems to have some functions to query data, but I am not sure if it will be enough. The second problem is the extraction of the keywords. I have and know a couple of of games that I could extract stuff, but since it is a lot of work, it could be interesting that other people join the project to extract keywords. So I will need a way for them to feed data into the database and to control the quality of the information. All this demand a lot of time which I am not sure to have.