What if saved APs will increase your sequence, so, for example, you have 16 sequence and he has 20 sequence. Each unspent AP will give 2 to sequence.
His turn 1st, because he has more sequence:
He shots at you losing all APs, or leaving 1 AP, his sequence is 22 until his next turn.
Then your turn:
You burst him and leaving 4 APs, you doing nothing, skiping your turn, so you have 16+4x2=24 sequence.
End of round.
Your turn 1st, because 24>22, so your turn again and you can burst again, and then keep these 4 APs, or else he'll have double turn, because his sequence will be higher and next round he'll have 1st turn.
If you want X-Com/JA2 system, then sequence can be used to intercept turn after each action someone does by sequence roll of action maker against other targets. Number of critters/player who see him will be added to action maker roll, because it easier to do something when there're alot people, because it's impossible to recognize who's hostile, who's neutral and who's friend, so high sequence will allow to you to observe doorway with full APs incase if BGer with lower PE, meaning with lower sequence will go throught that doorway and sniper will have a roll to intercept turn and can make a shot, but... it more looks like Fallout Tactics, not Fallout + it's TB... I don't think you'll see much cool battles in TB.
About unspent APs... only because almost noone is using TB it won't affect anything really, even caravan traps in TB, because there's no more visible caravans on the map.
Anyway it'll be useful for critters, even non-melee, if your weapon has range more than thier + not all critters shoot on max distance, so these morons sometimes lack ~1 AP to hit you while you using hit and run, so with this it'll be harder to exploit lack of brains in critters, but really.. it'll only make battles longer, because instead of hit, run, hit, run, hit, players will use hit, run, run, hit, run, run, hit.
Also all I can see with AP saving is:
BGer hiding behind corner, skiping turn, then running closer to his victim with 18 AP (12+6) [or with 21 AP, if he has jet+action boys], then skiping one turn again and then running in point blank and bursting.
The only problem that such fights in TB in urban area with building with alot people in cool gear isn't that often, so you'll see that implemention once per year.
