[Inziladun]

As an aside, I did not review this long thread, so apologies in advance if I repeat anything unnecessarily.

Originally Posted by alatar

Or, maybe Eru has gone what we would call insane, and so has set the world on auto pilot and has mentally retreated into the being that is Tom. Running the universe surely has its down days, and maybe Eru got so bored that It decided to go native, as that would be more fun, especially if It could somehow fool itself into playing at being a being like Tom. I would not limit the abilities of a god to not be able to pull off such a deception.

If Tom is Eru's little joke, he's been at it quite a long time by the standards of his Children.

But I had forgotten Bombadil, if indeed this is still the same that walked the woods and hills long ago, and even then was older then the old. Iarwain Ben-adar we called him, oldest and fatherless.

FOTR The Council of Elrond

For Elrond to call a creature old means they are old. 'Oldest and fatherless' I've always taken to mean simply that the Elves had no idea who he was or where he came from: he was just there.
During the time Tom was hanging out in ME, Eru was getting things done; destroying Númenórë and approving the plan hatched by the Valar to send Maia to Middle-earth to lead the fight against Sauron, among others.
That said, if Tom is Eru, I don't know that I'd be inclined to think him insane or 'native', uncaring of the playing out of the Music. Not, as you say, that it would be beyond the abilties of an omnipotent Creator to accomplish the running of the affairs of the world from his 'summer home' in the Old Forest.

Now, one thing that's always intrigued me is Gandalf's views and words regarding Tom. At the Council, he says basically that Tom is the one being who could trusted to keep the Ring without succumbing to its power, so immune that he would be likely to throw it away. The proof of that the reader had already seen: Tom held the Ring, put it on, and immediately handed it back to Frodo with no hesitation. Gandalf clearly knows the same cannot be said for himself, Maia though he is. Over the years that's caused me to let go of the 'Tom must be a Maia' stance I used to have. Tom's power and will must be much greater than Sauron's.
Later, when Gandalf's work against Sauron is finished, he tells the hobbits:

I am going to have a long talk with Bombadil: such a talk as I have not had in all my time. He is a moss-gatherer, and I have been a stone doomed to rolling. But my rolling days are ending, and now we shall have much to say to one another.

ROTK Homeward Bound

Gandalf is going to see Tom, and tell things he has told no one else? 'In all my time': does that mean 'since I have been here working agaist Sauron', or since I have been alive and conscious of my own being'? Why does Gandalf feel the need to do this? Could he be giving an account of his doings, failures as well as successes; a 'confession' if you will? And what does he expect Tom to say to him?

All that leads me to the conclusion that Gandalf appears to be reporting to his 'boss', and said 'boss' would have to be Manwë or Eru.
In the essay The Istari in Unfinished Tales, CJRT takes issue with the idea that Gandalf was Manwë, saying:

Manwë will not descend from the Mountain until the Dagor Dagorath, and the coming of the End, when Melkor returns. To the overthrow of Morgoth he sent his herald Eönwë.

And surely, Manwë could 'debrief' Gandalf upon his return to the West, as he probably did.
Conclusion? It seems entirely possible to me that Tom could have been a manifestation of Eru.

Originally Posted by alatar

And so why not have Eru as a similar triune god? It could then express itself as male in Tom, female in Goldberry, and even nature in Lumpkin. How better to see how the theme played out than to plant oneself in the middle of Middle Earth, and then be able to relate to the characters within, whether sentient being, animal/plant, or element?

The idea of Eru splitting into male and female sections that seem deeply in love in with one another I find more than a little distubing.
One the other hand, why not? If Tom is Eru, Goldberry must be accounted for as well, and that's as good an explanation as any.