If full nodes are still needed then they are still the slowest bottleneck of the system, the SW implementation won't improve the bottleneck then what's the benefit?
Anyway this is just a generalized talk, I am not aiming SW, just showing by changing the protocol you can do whatever thing to bitcoin. So a change to protocol should be very carefully tested and reviewed, but due to the complexity of the codes, the review will be quite difficult
What constitutes a full node might change over time, as more advanced features, like UTXO commitments, are implemented. But yes, they are still the bottleneck, and the SW doesn't claim fixing it. The benefits are those listed in the OP, on the picture.