I'm sort of split on this, and honestly it doesn't really effect me either way. The way my guild raids, and the way I play the game, getting to 54 traits for Mythic raiding progression really isn't that difficult. Looking forward, it looks a bit more daunting though, especially if they keep going with the 'endless' trait thing that currently appears on the PTR.
To preface, I actually think AP and the ability to always have something worthwhile to do is actually pretty positive for the game. Realistically, the only people this hurts a lot is those who are already going above and beyond. Essentially those that do split runs, have raid ready alts, want to grind our legendary items for their 'mains' in addition to getting reasonable amount of AP for them. This system, really doesn't hurt the majority of the player base because for them, I imagine just having something to gain feels good each week. When you start running out of things to do or you aren't seeing power increases (whether they be large or small), generally, I start seeing people play other games. This is why you see so many people at the start of an expansion, and you see jumps in activity during each major patch.
The reason I would ask for a cap isn't really to make it less strenuous on myself, but for other classes, especially those who have multiple DPS specs within the same class. Those very specializations that differ so much between encounters that one might be substantially worse than the other for any individual encounter. For me it doesn't matter because all I do is play a tank, but I'm sure many rogues, warlocks, hunters, mages, warriors and DKs know what it feels like to feel pretty far behind because you can't potentially easily swap to another spec.
A lot of these systems currently in the game are fine (in my eyes) as a standalone systems. Legendary items, AP, relics and so forth are all decent systems that I think add value to the game. I realize they push class fantasy, and trying to stick to one specialization, but I think all of those systems listed above actually hurt some enjoyment of the game when you combine them altogether with the model of trying to stick it out into one specialization.
I ponder because personally, while I hate the legendary system.. would it have been that bad if all legendary items were class specific, and changing specialization merely changed what the items did? I mean, granted I would rather legendary items be utility/defensive in nature, but if a system existed as such where they swapped their properties based on spec, wouldn't that be incredibly superior? The same goes for AP. To illustrate imagine if AP instead was just a pool that you had throughout the expansion, and when you changed specialization it just reset for you to put into your other trees? Would grinding AP be really that bad under such a system? I don't think it would be personally.
Overall the systems I listed above aren't going to change in this expansion because I doubt they are going to completely change their philosophy on them. Tweak? Yeah, but they aren't going to say what worked and what failed until they release the next expansion.
AP I think would work better at a decent cap each week. Failure to cap in any individual week would just be rolled over into the next week, so you never truly fall behind, you just have to work harder (when you have time) to catch back up. This would work much like the old conquest point system for PvP, except instead of just rolling over half, you roll over all the missed AP for the next week in order to make people feel like they didn't miss out. This removes the issue of people feeling like they need to cap each week, and allows you to set a reasonable amount of AP needed to effectively cap each week. The cap would also quite obviously be artifact specific.
I see a lot of numbers and stuff thrown around but I think if you had an expected amount of AP gained each week, and know beforehand what people would be at on each individual week at a maximum, game balance might be a bit better as well. Right now you have discussions of people claiming that 54 is needed for later Mythic Nighthold, just like you needed most of your raid around 35 to have a chance on Mythic Helya. Whatever they decide it to be, they could simply balance around a number and let excess points be the slow nerf to an instance that they probably intended for it to be.
I'm arguing more for a cap because I think it potentially makes game balance better and even with a cap there is plenty to do in this game (at least how its setup right now) to grow in player power, which is what I think most people like about this expansion.