I currently use a maxpedition messenger bag, and it's entirely too large for my daily carry. It's part of the reason I haven't grabbed an LTT Backpack yet. I'd love the "steam deck" sized bag only if it could also accommodate the 40oz water bottle as well(perhaps with hook and loop fasteners to help secure different sized bottles). If that's a deal breaker for that sized bag, then I'd absolutely be interested in something between the sizes of the smaller bag and the LTT Backpack as long as it can accommodate the 40oz bottle.
Perhaps a compromise of doing one bag first and then the other later would satisfy the need people have to just carry a laptop and a few other things as well as those who don't need to carry a lot. In that case maybe the messenger bag first?
Either way, I'll be following updates for this very closely as my current bag is slowly deteriorating.