The FT-5 is a solid platform, with proper upgrades and a 32 bit board, CoreXY doesn't offer much more than what the FT-5 already has as far as print quality and speed.
I really want to see a large scale delta using 2040 extrusions and mag-balls as well as a 300mm build plate, with the option of a flying extruder and piezo auto leveling system.
The absolute optimal setup would be- 2040 extrusions, linear rails, smart effector, pully assisted flying extruder and a duet control board- this would not be a cheap bundle, but it would be much easier to setup and would have a higher success rate than a typical, bare bones delta and much easier to build and adjust than a coreXY.
The only hurdle is getting FT to carry Duet products, they are not cheap but support, ease of setup and performance is second to none.
The Duet forum are mostly Delta users, most all machines are custom, there is not much out there in a way of large or high-end delta KITS, there are ready made models in the thousands or outdated Chinese examples.
I like my cuboid printer, but it's time to revisit the unique delta.