I don't know about the i2k. With the new tfm stuff I heard that Meduza has been printing pla for 1000h and I heard that other guy has wore out his at 2000h print time. I like the idea of i2k but in my experience it needs a tighter setup, enough to cause deformation on the tfm (again it just my personal experience) I love the i2k but only if you will be printing at 250C + for long periods of time. I seen that i2k increases slightly the force needed to extrude and I need 3-5C more to get the same gloss finish (using Faberdashery). Does it work? Indeed. IMO I had to drill the tfm/i2k after doing a good sandwich to make the extrusion work perfectly, but also since I use 1.75mm the gap it's smaller and more reluctant to suffer since 2.85mm filament works a coupler/nozzle with more room to play with (3.2mm) 0.35mm vs 0.25mm of room for the filament.
I think that with a fixed spacer and tfm aloneyou will do just superfine for a really long print time.
About the v3, unless you get the new nozzles I don't see any advantage on the design.
Also about the flexidrive. I heard very ugly stories about it and the many problems the small plastic gear give. On paper sounds fantastic but imo it's more a pain in the butt than a good printing sollution. I would just buy a pancake motor and a titan extruder and attach it to the hotend. That would be around 60€ of easy and reliable sollution. Ofc, it weighs quite some, that's why I'm waiting for Anders small and little weight sollution for the pancake drive. But for me with the cheap bontech + the FatIRobertI I designed it's more than enough for my needs (I been printing flexibles at 40mm/s with some retractions without oil) and willowflex I can print it at 60mm/s with hundreds of retractions.
Well that's my 5cents of opinion