Any one make such a thing? I’m thinking that the bag would have another sewn in attachment point, that you could clip another strap to and wear like a rucksack.

I have no doubt that a ‘proper’ rucksack is the best for load carrying/comfort but I’m thinking more about city use/exploring new towns whilst on holiday etc where rucksacks are frowned upon. A messenger size bag can still become heavy on one shoulder so I’m thinking that the option of carrying it like a rucksack for a while would be a nice option.