Hey, welcome to T3A and the AotR community.
It's not a matter of ambition, really. It's a matter of which idea we like the most.
We think Frodo is the perfect Ring Hero for Good factions because he *was* their Ring Hero - he saved Middle-earth thanks to his immense inner strength. The exception is Erebor, where Bilbo is the Ring Hero, because Frodo wasn't born during the era our Erebor is set in, and because he, in a way, was the 'Ring Hero' of Thorin's Company, saving them on multiple occasions thanks to the Ring and his strength of character. We like using those very Tolkienesque themes and turning them into gameplay elements. "Even the smallest person can change the course of the future" - we're suckers for that sort of thing and even though AotR is a mod for a game which is all about killing your enemies, we took this opportunity to imbue it with some Tolkien spirit.
Same goes for Sauron. If Misty Mountain orcs got the Ring, they'd hand it over to Sauron, unless Smaug claimed it for his hoard (which he does in AotR ). If the Haradrim found the Ring, Sauron would most likely get it too, especially now that we've decided to give them a Nazgul-in-disguise hero, the Golden King. The only exception here is Isengard - it seems more Tolkienesque to have Isengard get a super-powered Saruman, because Tolkien implies Saruman would have been able to bend the Ring to his will. Still, Saruman is already a regular hero, so we'd have to either remove him or create a complicated mechanic like an option to 'buy' his Ring Hero form after you have the Ring and Saruman is already on the field, otherwise Isengard gets a crazy advantage. So Sauron it is - at least for now.
Your suggestions are interesting, but they're extremely far-fetched and all over the place, making various levels of sense (some making zero sense at all), and it seems to me there's no concept behind it beyond 'it'd be cool to see', in which case I prefer our attempt at injecting some of Tolkien's themes into the gameplay. In this case we think less is more, and that there's beauty in simple systems.