I've been trying to theory craft a hybrid champion for several months now, though i constantly forget to update my drawing board to tweak the numbers in my head. i can post the general outline as its scales and tuning still need tweaking for balance and effectiveness.
but in short it would be a bruiser Melee-healer. His passive would take a % of all damage dealt and damage received ( before resists) and convert it into an energy bar that can be used for either offense or defense. the % ratio would decrease as the game progresses based on ap/ad/resists to reduce scaling and keep the passive gains controlled. this function allows him to feed his passive for damage or heals and gives purpose for him to tank and/or deal damage without relying on either.
he would start with a well of 250 "power" which would increase by 250 every ~ 4 levels, maxing at 1000 at 16. His basic skills will only empower by 250 "power" unless using his ultimate. his ultimate will allow a burn of 750 "p" on first basic and 500 on the next skills. Ult deactivates after 10 seconds or 3 seconds after having used every skill once, but not exceeding the base 10 seconds. Ultimate increases defence, health, ap and ad by acceptable amounts. 10 second window or upon using all skills once keeps the steroid from being over powered by giving him a choice on how to make use of it. either by using it for the steroid of for the skill empowerment for additional damage and support.
from there he would have the option to target enemies with certain skills to deal additional damage or cc and target allies to provide a heal that would function as a health battery. ex. 1 ally in 250 units receives 100% health, 2 allies in 250 receives 50%. further delineation could go so far as to make the pool heal champs to an = % before raising them both, which could provide additonal support to those dying. he would not be allowed to heal himself. life steal and spell vamp only.
80% of his skills would have little to no base scaling and would rely entirely on his build with bonuses applied after reaching benchmarks. as an example for every 50 ad his ad ratio increases by .15 or such. same goes for ap. this increases either his healing or damage ratio.
this allows a melee to deal damage, and provide support to the team through cc and heals at the cost of forcing him to be in melee range for it and to potentially sacrifice itemization that would make him truly tanky. he has to survive team fight burst but only long enough to be useful. hence the passive that feeds both on damage and defence. long team fights mean more utility, but high tank stats mean low quality skills. poorer heals, damage, and potentially cc.
example of team heal. 100 health at lvl 4 + {100 x .2 base ratio^increased by .05 per 50 ap("p" spent [0-750 during ultimate first cast])
lets say with lvl 4 and 200 ap that becomes a 130 HP heal without his passive. with an ultimate first cast it becomes a single shot nearly a 1k Hp heal battery for nearby allies, prioritizing lowest health first. but at the cost of losing the first shot benefit on other skills. his passive will be intended to be used every time he uses the skill on an ally, so the passive bonus can make it range between a 150-400hp battery without ulting. making it decent unless in large crowds with = health unless someone is clearly lower that will receive priority. cooldowns and gameplay would clearly come into play as well to account for the strength of the skill as well.
but like i said. i need to refine my numbers, but that's the verbal outline of the plan.