Dragonblade
Adventurer
hong said:6 + Con mod hit points of healing would be piss-poor at high levels. Sure, they appear to have scaled hit points back, but healing 10 hp (18 Con) is nothing when you have ~100 at 20th level.
I suspect it'll be 6 + Con mod times/day, with a limit on how often you can use it. Most likely it'll be 1/encounter as a default ("second wind").
I agree with you most of the time, hong, but I think you are wrong here.

Your example of healing 10 hp at 20th level is mistaken. You would heal 6 + 4 (bonus from 18 Con) + 10 (1/2 level) for a total of 20 hp healed on a surge. And a 20th level Rogue with Con 18 would have 111 hp. 20 hp is almost 20% of that. That is a reasonable amount to heal on a surge.
I think healing surges will not be tied to any per day mechanic, other than perhaps second wind being usable once per day. But even then, I wouldn't be surprised if second wind is once per encounter, just not triggerable unless you are bloodied.