Hi Guys:)
I'm just freshly bought myself in the beta, but I was watching the development, and now, I have time to read through the forum.
For the record, I'm a Land Surveyor Engineer, and Laser Scanner Operator. I working with 3D models and 3D city databases all day long at the office, so I know quite much about the GIS and carto bacground of these questions.
For the first idea, I think about that, 3D would be nice for OWM. Now, I read the thread, and now, I think, 3D would kill OWM. I see the potential for GIS use of OWM, but the 3D is a hard nut to crack.
During the reading of the previous topics, I see that, ppl love to make maps, for fun, for a journey, for D&D, and so on, and OWM is perfect for this.
3D could be fun, but not in this software. In my point of view, another software with a different name and different goal to achive can do more, than expand OWM with 3D functionality.
2,5D would be interesting. For first idea, I think about fixed viewpoints to make maps a little more realistic, but I don't know much about this.
But, I had another idea about this. As far as I checked the software, there is no contour line drawing. The contours and/or shadows can make a map more realistic. The other way, which would be nice for OWM height display, is one very old way from the old Hungarian maps, where height was displayed by small lines, where line weight and direction could display the mountains. See on the picture below.

OWM is a good map drawing application, but as I wrote before, it's simple, and this is good. I prefer for a software to handle multiple file formats, have a lot of functions, but in OWM, I do not require these. For the success, I think, small improvements and stable operation is much more important, than great upgrades. I saw some GIS softwere, where greater updates were much more important, the solve smaller bugs. OWM can run a great success, when reach official release, but overall, 3D is not suitable for it, according my opinion.
Please don't forget, this is MY point of view:)