I've made a new character recently and through the hard times of low-leveling I got curious about the feats.
"Once per day, as a free action, the character may heal a number of hit points equal to his Constitution modifier (minimum of 1)." Of course, being healed for a constitution modifier might not seem like a good deal to make for a feat: the maximum constitution one could have would be 25 base + 7 with max con buff + 10 with barbarian rage, + plus maybe some shapeshifting and some UMD things, so I'd suppose the maximum one could get at lvl 20 would be about 30 HP, which is not half of what the said barbarian would gain with his/her rage con. boost. So I thought to myself "maybe you can use it when your unconscious", so I tried, even if it sounds ridiculous, and it didn't work. Worse than that, I get called a witch by local Barovians for a feat which heals 2 hp, but that's another story.
All that to say that no non-healing classes would take such a feat at the moment. My first suggestion would be to augment the healing power of the feat. Though I don't know the full capabilities of the system, I thought of using the 5th ed DnD player handbook (as I believe the feat was taken from) and simply adapt it to the online game, considering the HP per lvl is not the same as the table game.
It would go as followed:
"Once per day, as a free action, the character may heal a number of hit points equal to its hit dice(i.e. character lvl) + its Constitution modifier (minimum of 1)."
Another idea would've been to replace the amount healed by:
(A fourth of the hit dice+1)*(the class hit dice i.e. 1d12 for Barbarians or 1d10 for Fighters)+ the constitution mod., but I doubt it would work.
Also, to remove it's spell property, as the character would heal from his/her inner "pool of stamina", as I believe it's said in the 5th ed.
Thank you for considering.