It is probable that nobody remembers me, but I decided to return from the dead to post in this thread and then disappear again for a while. I would probably say that category 1, time, applies to me, as I've only been able to play a few gunboat and live games very sparingly over the past few years.
I) Maybe gunboat cannot be properly categorized as Diplomacy, but the same thing can be said about Webdiplomacy. Who really Diplomacy plays with 72 hours turns, possibly taking 72 hours (due to either strategy or procrastination) to make an obvious disbandment. If you play it live, then there are additional elements to consider. You can see which players are talking to each other and determine which players aren't available to talk to you in the frantic time period between turns (games by mail aside). You can watch for tells that a person is lying. The best liars on this website might not be so successful in real life games. Gunboat in particular is sort of unique to online Diplomacy - it would honestly be weird to play in person. Maybe Gunboat is not real Diplomacy, but neither is WebDiplomacy. I suppose you could still make the distinction that Gunboat is still not quite Almost-Diplomacy. With all of that said, I've mostly played WebDiplomacy myself and consider that to be the real Diplomacy, however, I would opine the same about Gunboat.
II) Whether and how variants in general can be considered Diplomacy might be another area worth exploration.
III) One of the few games I've played in a long time was a gunboat game, and that game was one of the most exciting games that I've ever played. As Russia, I allied with Turkey (we shared some supports), only to be attacked by England from the outset and subsequently stabbed by Turkey and then even attacked by Germany. Italy refused numerous invitations to an alliance. Meanwhile, France took advantage of Germany and England while I managed to rekindle an alliance with Turkey after having been stabbed, acurately predicting the necessary shared supports. Just before France was about to win, Turkey, Italy, Germany, and I suddenly all at the same time put together a pretty good stalemate to stop France for a while. I went from having 2 supply centers in a gunboat game to having 9 supply centers (second place) in the eventual draw, with perhaps a long shot at a win if I had continued.
/End of monologue + back into hiding for a few months until I randomly decide to play a short game or post in a random thread.