I have tried normal parley way back when the game just came out and was not even working properly. I have not bothered to play it since, outside of when I am forced to in the storyline quests. The results were something like this.

Win-get back initial wager item (no reward)
Win-get back normal quality version of wager when betting a high quality version item
Lose-lose wagered item

I sent a bug report and it was clearly an unfinished product. It has an ability tab at the bottom that is grayed out if you bother to look. Your ideas do seem interesting but the part about PvP parley would be pretty difficult to do with parley the way it is. Even if each player simply chooses the best possible combination of icons, it is simply a matter of luck in who would win and who would lose based on what random numbers were generated by the computer making it a game of pure luck/no skill. The computer AI can also be justified as horrible as 10 star parley opponents still don't select the best icon choices available during their turns. It might involve more strategy if perhaps the next 3-4 icons that would load were visible at the side and such so that you could set up or prevent good icon sets for future turns. Parley is just seriously lacking considering it is the official mini-game of Eorzea and it's forced on you in about one third of all storyline quests.