As you said, this would encourage camping and whole combat would be slow-paced.
Defender wont be able to respond to any attacks, because attackers will flee immediately after.
Having more static game is not good IMO.
Your solutions are pretty complicated, I doubt they would be applicable in near future.
On the other hand, I agree that walking should have some benefits, but I think we need different approach. Like implementing stamina bar from D2. Or promoting walk feature more f.e. with less visibility (making less noises, less erratic movements) / higher AC.
NOi think if we put an AP regen on the walkers this will be good
Stamina would make group managing harder because chars with low stamina would lag behind. In the end, what purpose would it even serve if certain players couldn't run nonstop? It would too slow down gameplay because players had to stop and rest but without tradeoff. If running took your aps, the tradeoff is that when you run, youre fast but unprepared.
or make like in Runscape, have 100 run points that recharge
Well its matter of balance. Stamina would be derived from endurance, but no one said, that low endurance would mean low stamina, thus being almost unable to run, it would be just lower, meaning you cant run around whole map all the time. Or stamina could be the same for all, but regen could be affected with endurance.
Youre forgetting about key element of PVP - rushes. If group of people is rushing towards the enemy, they cant afford stopping next to them and waiting for APs. Even now is rush one of the most complicated move to make in pvp.