I do like the idea of B, it's just the implementation of it that I am a bit sceptical of. I like Lowe's idea of(posted 9286 days ago)-mt for a marathon game attempt and perhaps -tm for a tournament (5 lives only) game attempt. And then there are games like Tetris which are marathonable but where you only get one life or limited lives anyway? My list of marathonable games include Defender, Joust, Robotron, Gauntlet (depending on settings and initial screen sequence), MrDo, Asteroids, Bomb Jack, Tetris, Track & Field (which I gather has been made one round only).
One point I have do have for marathon games though is that they can be a battle of wills. For example, I feel I can beat the Universal Mr.Do high score (6.2 mil) but I can't be bothered at the moment so Tim Hood is winning the battle of wills for that game. Pac Man is another example, although you do have to score well up to the ninth key. If Mr.Do was made 5 lives only it would not be like it would be in an arcade but it would mean that more people would have the time to beat the high score.
Another point is that if games where you get an indefinite numer of lives were made 5 lives only, it would change the way risks are taken to get those extra lives. For example there would be no need to take risks in going for the 'E' coin in Bomb Jack or the 'EXTRA's in Mr.Do.
PS. Wasn't one clone of Joust supposed to have been moved to 5 lives status by now?