That's a good question; let me speculate a bit. I will put the majority of my development energy into the software running on my primary smartphone. Currently that's the N950 and seeing how lovely it is I'll try to keep a hold on it as long as possible
The QML based Marble Touch shares a lot of code with the original Marble application -- after all the major part of Marble is the marblewidget library. The user interface however is a complete rewrite, so porting improvements to the (original) Fremantle version would mean to implement it separately. For portrait mode this may be easy to achieve; I heard that Bernhard has enabled it on his N900 and it works fine. If it doesn't need too many changes, I might introduce it in one of the next minor version updates even.
Another way to port things to the N900 would be to port the new Marble Touch application to the N900. That mainly depends on the Qt Quick / Qt Components support for Maemo.