The Zesty Nimble looks interesting, just not quite sure I'm convinced that the flex-drive mechanisms have proven themselves yet....
At the moment, I'm thinking I'll end up doing a "cold turkey" CoreXY conversion. I'll finish some minor things on my stock FT5, such as mechanically linking the Z-axis rods and installing a reverse-bowden filament guide to improve reliability, but otherwise resist the temptation for incremental upgrades until I have everything together (and printed) to change everything at once.
Long-term, I would like to do the following:
* Replace all structural melamine parts with aluminum
* Replace or improve the stiffness of the bed
* CoreXY drive mechanics
* Single Z-axis stepper
* Convert to a geared bowden extruder with a lightweight hotend
* Return to a side-mounted filament spool holder
* Remove the part cooling fan and ductwork, replacing it with a Berd-Air (or equivalent DIY) compressed-air part cooler, supplemented by a fixed "general air movement" fan on the side of the chassis.
* Remove the cable chains, and secure the hotend wiring, bowden tube, and part cooling air tube together as a single arched bundle
* Remove the extrusion from the X-axis, and use the linear rail as the sole span. (Enabled by the extreme lightening of the print carriage from the above mods).
I'm also considering narrowing the frame. This would be accomplished by removing the two extrusions which support the Y-axis rails, and instead attaching those linear rails to the extrusions on the outside of the frame. Likewise, the Z-axis rods and the like would then attach to the bottom of that same extrusion and the top of the base extrusions. Somewhere around 70-90mm could be trimmed from the width of the printer in the process, subject to the design of the X/Y axis structural connections.
Or... just building a second printer with the above changes all rolled into it.