A mini-series could be an option as well.
The biggest reason I feel a long-running tv show won't work is because of the reasons I stated earlier. Serialized tv doesn't seem to work anymore. With some exceptions ofcourse, most shows fail after one or two seasons. I'd hate to get my hopes up with a new show, only to have it cancelled after a while. I do see how tv-movies couldn't work well either though.
So perhaps, a mini-series of 6 episodes, telling a story from beginning to end, might be a good option.
1) Who says the new show has to be serialized?
2) Serialized shows aren't cancelled more frequently than other shows. Most new shows are cancelled after one or two seasons. That applies to serialized, episodic, dramas, sci fi, and comedies.
3) Falling Skies and Walking Dead are doing just fine as serialized sci fi on TV these days. A network exec is a lot more likely to copy their success than try a format that has been DOA recently.