As a TTer and not a triathlete, I am never going to attach a bento box or other bag to the area on the top tube that sits behind the stem, but
what I would love to see is a "mini water bottle" that would sit in that area. The cage would be similar to an Arundel Chrono, in that you would just snap the bottle into the cage (the fact that the bottle would lie horizontally on the cage I would think would make it less launch-prone). It would be better than a BTA setup because not everyone has room between their extensions for a BTA bottle, there can be computer mount issues with a BTA setup and getting the bottle in/out would be easier than with a BTA setup (and would not affect steering).
I know there are some who can do a 40K TT without liquids, but sadly I am not one of them. This would be great for that and even the 20K -ish TTs where you may need a little drink here and there, if only for psychological/comfort reasons.
I'm not sure if there is enough of an installed base of P5s to justify developing a product like this, but I wish it existed.
Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152 https://vimeo.com/user11846099