For my first Stayer (the green bike) the hose exits the down tube just before the BB on the side/top, then enters the chainstay on the top just after the BB (and out again on the top just before the caliper). So kind of like your solution but going above the BB instead of under. It's neat and I like it.
For my second Stayer (the sparkly bike) the hose exits the down tube just before the BB on the bottom/side and is then routed externally via one 'hook' (no zip-tie involved, not sure how it's called) put under the stay, under and on the inside of the chainstay to the caliper. So kind of like this solution but without the routing through the stay. It's also neat and I also like it. (The hose is black on sparkles so not really noticeable - and covered in mud most of the time. I should really take the rear caliper off anyway)
To me it seems the 2nd solution achieves much of the original intent (by going on the inside of the stay the hose is nicely hidden away, even if it isn't actually internally routed) with less faff than the first.
For my first Stayer (the green bike) the hose exits the down tube just before the BB on the side/top, then enters the chainstay on the top just after the BB (and out again on the top just before the caliper). So kind of like your solution but going above the BB instead of under. It's neat and I like it.
For my second Stayer (the sparkly bike) the hose exits the down tube just before the BB on the bottom/side and is then routed externally via one 'hook' (no zip-tie involved, not sure how it's called) put under the stay, under and on the inside of the chainstay to the caliper. So kind of like this solution but without the routing through the stay. It's also neat and I also like it. (The hose is black on sparkles so not really noticeable - and covered in mud most of the time. I should really take the rear caliper off anyway)
To me it seems the 2nd solution achieves much of the original intent (by going on the inside of the stay the hose is nicely hidden away, even if it isn't actually internally routed) with less faff than the first.