> Would that be, to all intents and purposes, undetectable by us then?
In so far as our means for measuring particles doesn't change; namely, smashing things together at extremely high energies.
If you suppose that there are methods for measuring sub-Planck length areas then one must assume that they involve either: energies lower than those believed to be needed (which doesn't necessarily come to a solution, but pushes the problem to even higher energies and shorter lengths) OR that there is a default force that keeps space-time stable unless high energies are approached.
Note that both notions are mere speculation, the first on logic and the second on intuition about phase changes in states of matter.
Would that be, to all intents and purposes, undetectable by us then? If so then that might be a possible explanation of "dark matter", assuming all these things were individually smaller than the Planck length.