That would mean that you need a little less than ~70 Transcendence to Incarnate, since Level 6 is a DC 80 check. Not that that's a bad thing, necessarily.
First and most obvious remedy is to make the checks all have modified difficulty, rather than just being "Your mind" or "The new vessel's Body". In the main thread, you told MJ that building a six armed body would require a check of 30+Body Stat; why should it be any cheaper if you're in the Deep Sea? Similarly, any character who's focused on Transcendence will have thirty points in it at least. Make the mind check have a base of twenty or thirty or something. Maybe more, if you wanna lock it to higher T people.
Maybe say that when you're dead, you can only take one action per hour, which means you take one mind damage per action. That at least ensures people will be hurt before incarnating, while still allowing someone else to come in and rescue them. Another option would be to say that when you Incarnate a new body, you take permanent damage to your mind stat to pay for it; that'll result in everyone incarnating into 1 Body bodies, but it's still a massive nerf to incarnation.
Actually, having permanent stat damage upon death would be a great idea--the Roa Deathless entry mentions how they're continually revived until either the body or mind is broken, but the system as-is doesn't cause you any permanent harm. Making death actually harmful would make that entry make sense. It would also make sense if you can't possess arbitrarily high Body bodies, instead being capped at your original Body (which lowers with every death); this at least means nobody will engage in shenanigans like I am, where you start with 1 Body and then get placed into a new custom body with 20 Body or something.
@Errant Ocelot
The other option is "Everyone is immortal", which while perhaps an interesting game concept, is not at all what this system is built for. Kinda sad, I think it would be neat to see an ER style game which is built to handle everyone being capable of reincarnation.