By encoding I mean representing bits of information as some form of mass-energy that can be, at some time in the future, decoded back into the original information bits without loss. This does not imply that the physical form is containable, just that it is predictable with respect to a given volume of spacetime.
Let's assume that 1) the volume is one cubic meter, and 2) we're not constrained by current technology, only by currently understood physics.
For example, would the limit be the maximum number of photons that could occupy a cubic meter at a given time? Where, say, the presence or absence of a photon at a particular location within the volume at that time would represent the value of a bit? If so, what is the bit count of that limit?