Effectively the prestige system is a way for any bio to get what ever ability they want, outside of having a hiruko bio, or winning the prize in a tournament or event.The premise of the system is super interesting but it seems a bit...complex and I didn't understand some things about it.
Long ago, someone suggested, dont remember who it was, that sages would make a bio that was "themselves" and that they could build upon. This bio would either be from their CC (if they had one) or have the same structure and make up of a canon bio but with the sage's story in NB, his look, etc. After having this bio for some time, people would be able to use stuff like genetic implantation, eye implantation, etc to grow it if feasible as long as such combinations were possible in NB.
So, for example, in NB at the time you had Wood+Sharingan in some bios as well as Wood+Rinnegan+Sharingan. You'd be able to make a CC bio that could receive a Sharingan and Wood DNA implantation. However, since there was no Byakugan + Lava for example, you wouldn't be able to combine those.
At the time it was deemed potencially too broken. The power level of the RP was simply too low to have bios running away like that. But for me, the RP aspect of gathering DNA or Eyes from people to build on your bio using official battles and RP was very interesting. As well as the idea of a Sage having himself made into a bio with the abilities he wanted and was known to use.
With the current RP kumi system, this could be a nice way though to monetize (kumi wise) some things. For example, if a ninja can gather DNA from someone but he doesn't have Medical Jutsu to implant it he can pay a member with medical nin to do it. Or you could trade DNA ou Doujutsu through Kumi. There would be interesting aspects to it. Broken and not possible in the RP, perhaps. But interesting nonetheless.
So you could make combinations that arent possible, eg you could make a custom Madara, EMS+Rinnegan plus say rain or puppets etc. Additionally, They also introduced Canon Advancements, so that you can use techniques that are character specific. So instead of having standard or custom ems, you could use Sasuke EMS or Hashirama level wood instead of regular wood. Now that YinYang is obtainable by anyone and everyone via the kumi system, it opens up new pathways for people to create the bio they specifically want.
The only downside at the moment that I can see, is that you cannot add abilities that are specific, so eg Flying Thunder God, Chakra enhanced strength, etc, because its not listed as an 'ability' but more a character exclusive technique.
However, I think it would be pretty fun to be able to make a prestige bio that is a jinchuuriki as well, with EMS. Imagine that! lol
There are plenty of interesting combinations you can create, the limit is just the points system, and you can only have 2 of any type of ability, so 2kg+2ha+modes etc. The rank up system as well rewards using your prestige bio and actually being active, not requiring kumi to advance your prestige bio.