Sorry this is a bit late.
There must be quite a lot of us 60-something cavers around who gratefully took up SRT 30 years ago when ladder climbing was becoming too much like hard work, and are now at the stage when they still want to do the SRT classics but not much else.
They no longer go to places where you need to lift a full tackle bag at arms length to get it through some gnarly traverse/squeeze so they don't need 3 or 4 handles. Or perhaps any at all.
There are stacks of SRT trips in Derbyshire & Yorkshire where bag-handling in the cave just involves carrying it on your back, dangling it below you or dragging it behind you for short distances.
Being cavers they will still expect the bag to last forever so you can't skimp on material quality, but a couple of shoulder straps, a pair of loops for dangling, a draw string closer that just gets tied and a drain hole would do it for me. I would want it to hold 80 to 100m of 8 or 9mm. Or that nice Gleistein that's still so packable after a lot of use.
No handles, inside pockets, interior gear loops, flaps, fancy toggles, hauling rings.
Missing all those things out might make it possible to sell a bag far enough below the normal price to persuade us sad old gits (sorry OG) to fork out from our hard-earned pensions.