So I'm thinking that in place of Failed Careers / Starter Packages, there will be something like Poltergeist Forms, the form they would take in one of the Numberless Courts of Hell if they died, prior to reincarnating, if they for-real died, but these will include some items or abilities and a short roll table if starter karmic attachments, all of which tie into the theme of the Poltergeist form and collectively should give a GM an idea of what some Karmic Attachments might look like. Probably for this initial release I'll just do a handful. Then there will also be roll tables for Karmic Attachments that aren't as specific to a character but are more like quests or things the party can interact with. So you can still sandbox to an extent, but if you're really mucking about without resolving anything, you're going to accumulate too much karma. This whole thing is loosely inspired by my vague recollection of Tenra Bansho Zero, but in a way they're also kind of like aspects in Fate.
I'm glad you appreciate the ritual idea. That was also part of my thinking; reincarnation is a central concept of this game and setting, but I also want there to be real stakes where characters can die, besides just becoming an ashura (although that is also basically like dying). Of course, if they die but don't become an ashura, they could still potentially be found as a Poltergeist in one of the Numberless Courts and rescued, if someone in the party can afford that Karmic Attachment...