Under X11, and other graphics systems,
one can run emulators of historic video games,
work with console of ancient mainframes now tending towards dust and decay,
see the boot sequence of the old Apple ][,
use an old imaginary glass teletype by typing into a picture of one,
and scores of other things.
These simulations provide a link between the software of today,
and the software and even hardware of the past,
providing a sense of history and continuity.
More important than the feeling of nostalgia, however, is the the fact that these older interfaces, whether they be an obsolete game machine or a noisy paper terminal, were the environments required by software often still essential to some purpose today.
It would be difficult, although not impossible, to design a new interface paradigm from scratch, and then create all needed software within that new paradigm, discarding all known user-level utilities and tools from the past. A more consistant interface can be achieved in this manner, but at exorbitant cost, considering the thousands of tools that would have to be rewritten or totally redesigned to build a complete system.
On the other hand, by the simple expedient of simulating the legacy software's environment, almost all of the older software can be retained and made fully functional in the new medium. The process has already happened numerous times, from punch cards and lineprinters, to printing terminals, to glass teletypes, to intelligent terminals, to window systems.
This process is being seen again with the move to spatial interfaces. In particular, backwards compatibility can be expected with both window systems such a X11, and cursor-addressable terminals from around the vt52/vt100 timeframe and later as have already been simulated in X11. These two features alone, and the backwards compatibility with earlier technology that they themselves already evidence, will allow the reuse of man-millenia of software, greatly speeding the potential adoption of the spatial paradigm.