Previous comments by devs would imply this is not a Gen G/U edition. But that could havechanged if someone high enough decided they wanted more money.
It won't be one of the current spin-off series like Stories because that is already out in Japan. There is an unannounced MonHun game that Capco mentioned to shareholders at their last meeting. This could very well be the reveal of that title.
Timing could fit for it to be 5 as it has been 2 years since 4U and there are two MonHun teams (one for Gen, the other could have been working on 5).
It is too much of a coincidence that it will release in March. It will most likely be the reveal of the 3DS version of Gen G or 5 with a later reveal that there is a corresponding Switch versions. It could easily have cross-system support like there was for 3U on the 3DS and Wii U.
I'm a little torn on which I want it to be. I feel Gen could very well stand to have a G/U version, as there is a lot more they could throw in, but I want to see Monster Hunter 5. (I personally hope they have retooled the underwater mechanics to make it more tolerable for everyone and give us back some of those fun underwater fights and monsters).
I also want 5 to be a Switch-only title with better graphics and tech than what the 3DS can offer. Having both versions means that it will be limited by the 3DS capabilities and potentially be nothing more than an HD upgrade. There are a lot of little things that are very backwards in the series due to technical limitations. From limitations on monster behavior -especially the smaller creatures- to general graphical quality and the loading of different areas.