Summary
Thanks to those pointing me in the right direction (esp. regarding front center). Currently I'm thinking that this is possible without sacrificing agility or having too much wheel flop.
Since the original post I've found four examples of recent bikes that manufacturers have specced with high offset and slack headtubes:
- Rodriguez Phinney Ridge, see this article: https://www.rodbikes.com/articles/ph...vel-bikes.html They designed a fork for this model with a 55mm offset and they're suggesting using it on HT angles down to 70.5 deg for a gravel bike.
- Seven Matador Fork, a new carbon fork for gravel bikes, also with a 55mm offset. No mention of HT angle in this article however. http://www.handbuiltbicyclenews.com/...ke-gravel-fork
- Smaller sizes of production gravel bikes such as the Velo Orange Pass Hunter (thanks Ernesto!)
- Cannondale OutFront geometry as found on the Scalpel. https://www.cannondale.com/en/Intern...-geometry.aspx Yes it's not a road bike, and it's just marketing speak, but: "By using a longer fork rake to reduce the trail, we can exploit the stability of a slack head angle, without the sluggish slow speed handling usually associated with it. It's the best of both worlds: slack and stable on fast, challenging terrain, yet quick and agile at slow speeds and on climbs."
My thought on front center at the moment is that yes it'll increase by a nontrivial amount (+19mm) compared to my CAAD10, but I'm also used to riding XC mtbs with significantly more front center (+110mm), so how bad can 19mm be? Idk, we'll see.