Thinking about a bass module for the S1.
Many of us have B1's. That's about as small / light as we can expect and still get down to 40Hz, and have appropriate output to match the S1.
We also have A1 amps. All we need is a properly voiced crossover / eq to use with the B1 to get a good match for the S1.
If the crossover was available separately or in a B1 / A1 / crossover package, at a reasonable price, it might be a good seller.
Something similar, in a S1 dedicated and marketed package might sell better than a repurposed B1.
Of course to make this really work good, we need a bass line out on the S1. That would eliminate the need for outboard crossover and eq. If they had done this to begin with we wouldn't be having this conversation.
So maybe the answer is, redesign the S1 with bass line out, redesign the B1 to look like the S1, and put a battery in it.
I sometimes think Bose doesn't do well when making various components that work in multiple combinations. They seem to like unit construction and dedicated connections so we only use them in a predictable manner.
All that being said, I don't think a bass module bigger than a B1, but designed for use with the S1, would be a big enough seller to warrant building. That puts us right back where we are today with individuals making use of available components to satisfy their needs.