Anime News Network reports that writer Shoji Gotoh has started work on the final Full Metal Panic novel, though he doesn’t rule out writing additional short stories in the universe in the future.
Considering that the last I heard of the storyline, Sousuke & Kaname had admitted their feelings for each other, before current series antagonist Leonard Teslarossa had kidnapped Kaname and tricked her into thinking that she’d killed Sousuke (not to mention that Sousuke’s fellow squad member had been presumed killed in action – though we didn’t see a body), I wouldn’t mind getting some closure on that.
Plus, I presume that once the novels are finished we might get a fourth season of the TV series. Maybe. If they aren’t doing more Haruhi (which is genre) or K-On (which is not).