My guess is, you'll have the option to run through lowbie dungeons with friends one of two ways. #1: Level sync and continue to earn exp on your main (that you deleveled temporarily via sync for your friend). #2: steamroll them through the dungeon and not get much out of it (other than satisfaction of helping a friend). I will say that gear scaling NEEDS to be viable. FFXI was way too harsh with this. If you have a +10 strength chest, synching down to 25 should at least offer you 3-4 str, instead of 0 ontop of lower defense compared to a normal lv25 item.

I agree that level caps should go,on the condition that there is ample amount of content per each level range. The combined solution above should solve the challenge monger and the entitled steamroller issues at the same time

*edited for grammar*