Something I’d love to see, though I have no idea if it’s even possible, is a piece of interactive computer software able to represent the sorts of world models that physicists have in their heads.
That is, a model that has a bunch of “scale-specific compartments,” each consisting of some equations of motion or equilibrium or whatever, and each linked to one or more of the others by taking or relaxing a limit in one or more dimensionless parameters. These limits could be added in either direction, and perhaps even searched for over some space of equations.
One might have the ability, for instance, to have a single thing in the software’s ontology which has the property “obeys the ideal gas law in the appropriate limits,” and the property “behaves like a collection of many randomly moving corpuscles under the appropriate limits (not the same as the other ones),” and which knows how to derive the former from the latter, but can still use the simplified encoding of the former when doing other calculations that share the same limit.
Each part of a physical system would look either classical or quantum depending on which limit the user was using at the time, and they would do so together. Statistical mechanics would be (automatically) applied when, and only when, the relevant large-N limit was compatible with the rest of the calculation. That sort of thing.
To make things work out without needing too much pedantic formalism (or to extend it to areas that no one has rigorously grounded), one might need the ability to stipulate an asymptotic relation without proving it. But, in the cases where the relation came together with a proof, the program would be able to automatically compute and propagate some information about the leading order error terms in the various asymptotic approximations, which could be useful and interesting in a few ways – as a automatic check for common mistakes when making many approximations, as an automatic way to quantify the relative sizes of different effects on deviations from various equilibria, etc.
This would be nothing like a numerical simulation (which is what I usually think of when I think of software that represents physical laws interactively), and although much of the underlying backend would be something like a computer algebra system, the focus and design would be very different from existing computer algebra systems I’m aware of.

