Take a look at the work of various photographers and see whose work most closely matches your current vision, then find out what they shoot.
For instance, three colleagues here in Northern California who are tremendous landscape shooters are Elizabeth Carmel, Charles Cramer and Bill Atkinson. All three shoot MF digital capture and produce 30x40 prints rivaling 4x5 film. However, this route costs more than most midsize cars and that's before you add camera, lenses, filters, computers, file storage, printers.
You will be working very slowly and methodically on a tripod dealing with a system mainly optimized for the studio but repurposed for the field. Batteries last about 20-25% the frames you get with your D40 and file sizes can be overwhelming, and packing this stuff in the field will make your back scream, but that image quality.
You've better have a great market for your work or a large fortune for which to make your smaller fortune before you start in this direction!
One avenue coming to fruition is the Pentax 645 digital which Pentax hopes to get going for the many still shooting the Pentax 6x7 and 645 film cameras. Time will tell if it will gain a foothold as another digital MF contender. I know that there are still quite a few still shooting landscape with this system and then having their best scanned into the digital workflow and that's still a valid method.
That said, if your market for prints doesn't get much beyond 24x36 and you shoot more loosely, like the work of Galen Rowell, for instance, you will be perfectly fine with a FF camera or even the newer generation of DX cameras with selected premium lenses. Since one of my facets is shooting landscape (cultural landscapes for the most part), my D2x, D200, D700, and D300 are more than enough to produce quite excellent 24x36 (the right image with my 6MP D100 had this potential) and even a few 30x45 inch images. Granted, they won't have the same overall IQ that a digital MF can produce but with proper crafting and viewed from reasonable distances, they are still quite stunning and best of all produce enough sales to more than pay to keep my big Epson printers in ink and paper.
Why not take a MF digital workshop or rent a system and give it a whorl or rent a high-end DSLR system for a few weeks or take a workshop where they supply the equipment, try it and see for your self? The best way to really know is to put your hands on the stuff and experience things first hand or hang out with those that do what you want to do and learn from them.
From my experience is yes, you can do it, but know what are the limits then keep pushing them.