Okay so I'm trying to figure out the best way to deal with this and the possible issues involved.

Some of the flooring I'm installing will be ending at bathrooms where the floor is about a 1/4" higher than the tile. I'm also taking into account the high levels of moisture in the bathrooms and its effect on wood.

For this reason I was thinking about a transtionless joint between the wood and the tile. However, I not sure how to handle the height difference. Possibly route a roundover shape at the edge to create a gradual transition?

A transition piece is possible but since it will be partway into the bathroom it will be subject to moisture so I'm not sure it would be a good idea.

I could possibly make a transition out of another material (eg stone).

Any ideas/suggestions?

Probably you can route a roundover shape the edge to build a gradual transition between the wood and tile flooring.

Isn't the transition right at the doorway? That's where it should be, anyway. The moisture there would be minimal, so a wood transition piece would be the easiest to do.

The wood is going to take a lot of abuse if it sits higher than the tile. Then there's the potential for splintering. Especially if the end of the planks are running towards it. I would consider redoing the tile and making it even with the wood.