One of the fun things with the Micro Four Thirds (MFT) format, is the short
flange distance (20mm), which enables the possibility of making adapters for a number of formats. There are cheap, abundant adapters for many legacy formats, e.g.,
Nikon F and
Pentax K, to name a few.
When MFT becomes legacy
However, the flip side of the coin is that some day, inevitably, MFT is also going to become a legacy format. What happens with your gorgeous, and expensive, MFT lenses then?
Let's say that the worst case scenario is that, due to competition, the MFT system loses so much volume that it is abandoned by Olympus and Panasonic. It doesn't seem likely now, but stranger things have happened.
You can still use your old cameras and lenses, of course, but at some point you will want a newer camera, due to new features and better image quality. Can you still use your MFT lenses on some camera from another system?
If Samsung NX becomes dominating
The Samsung NX format is one of the competitors in the mirrorless system category. Let's say this format becomes dominating. Can you use your old MFT lenses on this format through an adapter?
In short: No. It's not possible. The Samsung NX format has a longer
flange distance (25.50mm), meaning that even if you made a very short adapter, the MFT lenses would not be able to focus to infinity. You could only use them as short focus macro lenses. Which is not very useful.
If Sony E becomes dominating
The Sony E format was introduced for their new NEX series. It has a
flange distance which is 2mm shorter than the MFT format. This is good news, because 2mm, while pretty short, is probably enough to make an adapter for using MFT lenses on Sony E. The Sony E format also has a wider flange diameter, which makes it easier to design an adapter.
However, the MFT lenses are pretty useless without the possibility to operate the focus and the aperture. And both are operated electronically, controlled by the camera. So an adapter must have the relevant software to interpret the Sony E signals, and translate them into something that the MFT lenses understand.
This kind of electronic communication might sound easy, however, it is probably far from trivial. And at best, your autofocus would probably be very poor, both the speed, and, possibly, also the accuracy.
For a comparison, let's consider the Canon EF system. There are adapters for using Canon EF lenses on MFT cameras, but none of them can control the aperture or the focus. So the probability of getting future adapters that provide this feature for MFT lenses seems pretty slim, given that there are many magnitudes more Canon EF lenses out there than MFT lenses.
Conclusion
The conclusion is that if the MFT system is abandoned, your lenses are more or less useless.
On the other hand, there are some rumors now that the modular Ricoh GXR system will include a Micro Four Thirds mount/sensor module. If launched, this will enable mounting a MFT lens to the Ricoh GXR camera, with an adapter mount/sensor module.
Update December 2010
Since I wrote this article, an adapter for using MFT lenses on Sony E cameras (NEX) has actually emerged. However, since it has no electronic contact, it can not control neither the focus nor the aperture. So you're stuck with a focus around infinity, and the max aperture. You can, however, use it with the Cosina Nokton 25mm f/0.95, which is a completely manual lens, with a mechanical focus ring, and a mechanical aperture ring.