I guess kicking people after 10 minutes is fine, if your not playing, don't see any reason to be taking up a slot.
Problem with reserving spots, is that it it makes the arena cap lose part of it's purpose. If you have an arena at cap, with 15 squads, and just say 8 reserve spots open, now you have a soft cap with 120 spot reserved. If the arena is capped at 300 HT is looking at an arena that is still 1/3 of the way open for squads. This in turn would reduce further the amount of people flying in other arena's. Also, it seems a bit unreasonable that a lone wolf type of player may be forced to fly in a certain arena because the only way he would be able to log into a larger arena would be by luck or by joining a squad. Though squads are great, there are still some who like the lone wolf style of play, and I'm not sure it is in the best interest of HTC to make a statement that squads are given better treatment than any other players paying the same amount of money for the same service.
That said, it might be interesting to use it as a side balancing feature. If you are flying for a lower numbered team in a capped arena, then you team allow for more players to log on and fly. However this won't fly, because many won't switch sides to begin with....though especially true if they have a number advantage.
If AH continues with arena caps, which I believe they will, I don't think you can take people who are in a squad and offer them more features than someone who has just as much right. Though it is unfortunate that some squads can't get all members together in one arena, there is still the option of changing arenas. If it is a big issue with you squad, you have the power to fix it on your own, if you choose. Though it is a compromise, it is also a solution. If flying together is a major issue....there you have it.