It's definitely a good idea, although it would be prefered to be a Tanky support with no damaging abilities who can old deal damage through auto-attacks.
I have some ideas for abilities for a manaless health scaling champion.
Passive - Curse of Immobilization:
Nearby enemies affected by crowd control are stunned for 0.1/0.17/0.25(levels 1, 8, 18) seconds. This can only happen to a target once every 10 seconds. (950 range)
Notes- I wanted an impactful stun that wouldn't be too abusable by the champion itself and would require some team follow up while still changing teamfights.
Q- Curse of Eternity:
Allied champion target only - 10% of current health - 21/19/17/15/13 second cooldown.
After channeling for one second target ally heals for the amount of health spent for this ability(10% of current health) plus 20/30/40/50/60 over three seconds . If the channel is interrupted, the entire cost of this spell and half of the cooldown are refunded
(750 range)
W - Curse of Misuse:
Passive
Nearby spell casts cost 2.5/5/7.5/10/12.5% more mana, health or energy to cast.
(950 range)
Notes- I wanted Curse of Misuse to be a passive so you wouldn't find yourself "cursed by misusing it" and missing entirely.
E - Curse of Ill intent:
5% of target's maximum health - 14 second cooldown.
Dashes a short distance, increasing armor and MR by 20/25/30/35/40 for 3 seconds and attracting all SKILLSHOTS towards you(this also lasts 3 second).
(400 dash range, 950 skillshot draw in range)
Notes- I wanted a gap closer that would be able to protect your teammates and provide you with the ability to pull off a nice ultimate or to provide your AD carry with the need support.
R - Curse of Chaos:
All enemies and allies in range - 150/130/110 second cooldown.
All allies in range get 100% move speed for one second and 50/65/80% attack speed for five seconds(You get this bonus too). Enemies are rooted for 1/1.5/2 seconds.
(950 range)
Notes- I wanted a mobilizing, engage/disengage that would be able turn the tide of a fight if used right. It's also the only ability the combos with your passive, ensuring that you will basically need your allies to back you up in team fights while you pull the strings for the front line.