It’s certainly a fascinating subject, one I hope to someday have a chance to study closely myself.
Before my editor or perhaps some of my wittier readers can get a word in edgewise, allow me to answer your second question: I believe so. While it’s true that the only known examples of the bond phenomenon in action involve a greninja, there really isn’t anything to the process that should limit it to just that species—or, at least, nothing to my knowledge. Likewise, the requirements we do know about are fantastically vague: bond phenomenon, according to old Kalosean texts (and arguably the known examples themselves) only requires a uniquely powerful level of trust between a trainer and a pokémon, although supposedly it helps to have a pokémon with unique special talents hidden deep within them. Of course, as with all texts, what those talents are has never really been made clear, and the only modern-day research we have on the process (from one Professor Augustine Sycamore) has not yet uncovered what that means.
Quite honestly, though, I prefer to believe it means any pokémon can have the potential to achieve such a transformation. Or, rather, that bond phenomenon is not limited to species but rather to the individual pokémon and trainer themselves. A special trainer would be able to draw out the latent talents of any pokémon, and thus, so long as you have that bond between them, it’s possible that a transformation could happen with any species, from greninja to rattata.
The Pokédex According to Bill 