I saw this section was looking lonely, so I figured I'd start things off. I'll add links when I get home: I don't have my computer here to remind me of the parts I used for all of this.
My 2020 i3 has been VERY heavily customized, and I'm really happy with the results. It's sort of fun looking back at this.
- Expanded the bed to 200x300mm (new heat bed, glass and aluminum carrier)
- Increased Z axis height to 260mm (size based on the end cuts from my Y upgrade and printed Z motor mounts)
- Fans on the X and Z motors (even with the voltage tuned down, they all ran very hot)
- E3D v6 full hot end
- 40mm print cooling fan
- Top mount spool holder with bearings.
- Stainless extruder gear
- Adjustable tension X axis belt mount
- Lead screws for Z axis
- Precision Z stop mount
And the end result is that for about as much $$ as the FT5, I've built something that isn't nearly as big and is way more fiddly to maintain 
I've also collected almost an entire printer from all of this, so that's probably going to be my next project... cobble together my own monstrosity.
