The X-Files managed to get get a couple of big screen feature films, why not The Walking Dead? I think it would be awesome, and it sounds like it could actually happen! According to Bloody-Disgusting, there have been "rumblings" among AMC and the crew regarding a feature film.
Now, nothing is official or set in stone, just people discussing the idea and possibility. The Walking Dead was originally being shopped around as a film before it got picked up as a TV series. If they do decide to move forward with a movie, the only way it could really work is if it corresponds with the TV series like the first X-Files movie did. It's got to continue the story of the TV series. They don't have to end the series to make a movie; a movie could actually help strength the series they're making.
There's a ton of material to work with so they could easily do a movie if they wanted, and I imagine it would be very successful. This may or may not ever happen, but it gives us something to talk about! Would you like to see a Walking Dead movie? How would you like to see it done?