The 2 slot in the N800 I think is enough due to the fact that the battery life would be decreased if anything else is added.
I can add a tilt sensor and IR to the N800 as well but I do not think enough people would want it for this tablet to make it cost effective. I would have to make another cover for the back of the N800 also and this would be expensive. I was however considering it before I received the N810 because I wanted to add a keyboard and Flash memory to the N800.

I also wanted the back cover of the N800 to be metal so I could use the magnetic cover without adding the metal pieces to the back.
If I thought enough people wanted it I could make an adapter to add Flash memory, Tilt sensor, and IR to the n800.

Most of All I think the N800 would make great a infrared remote like the ones that sell for $1500 but I would need the community to make the software interface to it.

I will be making some prototypes for this in the near future and if everything works the way I think it will, I will then wait for a response from the community with the software ideas and if they would want it.

Thanks all