That's exactly what I've been hoping for all this time, but thanks for posting it since I now know I was not alone with the thought (lol). Karma, in general, lacks a unique spell that would make you want to choose her over other options that pretty much offers the same tools she provides but with more reliable/convenient ways of delivering them. I feel that with her mantra-ed shield granting the main target a cleanse people would consider her more not to mention she would have a more reliable tool for support. I'm all for the idea and well, if it's never going to be considered by Riot, have the damage component returned and maybe tone it down to avoid making the spell the "go-to" choice for mantra. It opens up more combo options for her not to mention damage potential.
Another suggestion would be to have the AoE deliver a minor knock back to surrounding enemies, similar to Riven's Q. It would make sense visually and also gives Karma more tools for supporting since she lacks a hard CC to try to interrupt the enemies from focus firing on an ally. Every other support brings so much more that sometimes having to support as her feels severely underwhelming, like something's missing and is not quite there. She could use some minor tweaks to bring her close to being a solid pick. Overall, she's a great champion but one that's close to feeling complete.