Unless Bitcoin is replaced with a Bitcoin-compatible currency, I believe that all holders of Bitcoin will be out of luck when the day comes that it is obsoleted by a superior system, as inevitably happens in almost everything electronic.
Normally if a new commodity type is introduced into the market (such as the discovery of petroleum), the market will naturally find a new equilibrium, and this is not a problem. Normally when a new fiat currency is created, there is usually an exchange policy in which holders of the old currency are issued units of the new currency, but I don't see how this is possible in systems like Bitcoin. Nobody is going to want to trade units of the superior new system for units of the inferior system if they know that everyone in the world is going to stop accepting the old system soon, so everyone holding Bitcoin at that time will find that their savings are suddenly worthless if they cannot somehow be "brought in" to the new system.
As we know, the entire Bitcoin infrastructure is limited in currency units, which is normally an advantage because it prevents "money printing". Because of this, the only ways I can think of to solve this potential problem is if the new currency system has more units than the old, and when the old system is to be replaced, the developers of both systems coordinate to release a new version of their systems in which the new system is made to be downward compatible with the Bitcoin network, and somehow one unit in the new system is marked as unmineable and is instead replaced with the already mined units from the old currency system, which will probably result in forking both currency systems.
The consequence of NOT replacing one digital currency system with another is that either every new system or fork which gets popular will "print money" due to their creation increasing supply without proportionally increasing, or that innovation in digital currencies must be limited to things which are reasonably compatible with the existing systems. So if this problem cannot be resolved, it either means a slowing of the progress of humanity, or an occasional massive loss of purchasing power punishing whoever is unlucky enough to be a large holder of the old currency at the time that it becomes discontinued.
Is someone working on this problem, or are all the developers of digital currencies like Ripple, Bitcoin, Litecoin, and others simply betting that their system will be the victor for all time?