I have now been working on a media-server to do just that for a some time.
It currently runs on flask/python, (given the rights) will read directories and check for Information on imdb.com or thetvdb.com and save some of that data locally. It works with sqlite at the moment and used to hand over commands via dbus to vlc. It had full control and seek ability.
That was the simplest solution for me since I already had an unused PC around and hooking that up to the TV and Lan wasn't really an issue. It – of course – used massive amounts of power compare to what it did and the RPi.
So the new idea was getting a RPi and sticking that to the back of the TV and connect it via HDMI to the TV, the 3.5mm to the stereo (for mpd duty or backup-sound on video) and eth to receive playback-data.
But since the omxplayer didn't really offer any input other than direct piping I was kind of put off.
I honestly would love it if it offered something like dbus, but I realize this is a relatively small project.
I think joeh's approach is the best solution possible at the moment and if anyone is interested I would build that into my "media-server" and have a couple of RPi-users test it.
Actually, I am going to build it in no matter what, but I might clean it up some and polish it a bit if people are going to be using it

I have no timetable at the moment, but the first two weeks of August will be coding-months for me, so it might be a go then.
I'd be happy to discuss features with people, at the moment the server is supposed to
- handle a relative small db (that's why sqlite) that holds title, quality, size, description (and so on) for easy searching and playlist editing
- be able to control a media-player (this part is supposed to change to a class-based model to support multiple different media-players)
- have a templateable web-interface so you can have full-browser or smartphone controls and above mentioned db and playlists on there
Basically it should make it possible for you to control video playback on your TV. I did this because I was pissed off by disk-changing all the time. As it grew I thought why not make it even more extensive/informative than what would usually come with a DVD. Especially The TVDB was pretty awesome when it came to scrape information.
Sorry if I spammed this topic, just thought it was awesome that people already wanted to implement that and give my humble opinion and/or workforce to the idea.
Regards,
derdritte