What would be the point of such a change? The current away-mode works fine as it is:
One pays about 20 cents per game for a day's extension, so if I have my normal 6 games up, a 10 day holiday costs me about 12 euros, which is already a considerable amount. The 10 day auto-off is probably meant as a protection for a user's account credits.
Limiting the away time mode would reduce an income source for the development of this game (not a good thing), but I don't think it would bring people to book shorter holidays - at least I know that my wife would not take it too well if I would propose a shorter holiday just to be able to make my turns.
So we would see more missed turns then. Would that be a good thing?
Well, I am here to play interesting games that tickle my brain, but I am not here for gathering ladder points by free wins just because someone went to a 14+ days holiday. So I for one would rather wait for my opponent, and maybe just play another game of Warbarons against someone else meanwhile.