@B-Kinney While the current system is still legal, one way to reuse parts would be to give them to teams who cannot afford to buy new parts. (The starter kits have less than 12 motors, and many teams will still be using their existing kits even after V5 is introduced.)
Even after the current system is phased out, the parts could be used for classroom use.
Yes, I agree that would be one of the best ways to reuse the old system, but passing used parts to another team requires the trust between both parties and, at least, one of them to be good with testing and refurbishing, which is not something you would expect from a new team.
As for the reusing traded-in parts, you just had listed multiple reasons against it. There is no good business reason for VEX to wade into re-testing, re-certifying, and re-distributing old parts. I am sure the hidden logistical costs of doing that would be higher than anyone imagines and it might be even cheaper to manufacture a new Cortex if its components are at their lowest price.
However, if some of the parts on the Cortex' BOM are being discontinued themselves (and also Cortex specs are getting outdated) then it makes perfect business sense for VEX to incentivize people to switch to V5, remove old Cortex units from circulation, free up support resources and, eventually, discontinue Cortex production and warranty program.
In any case, for the purposes of this thread, lets assume that there are no more Cortex units and Primary Joysticks.
Now, what do we do with the remaining parts that are not V5 compatible?
The easiest thing is always to toss them into recycling bin and forget about them, hoping they don't end up buried in some distant landfill. However, part of this program is to teach students how to find creative solutions for diverse sets of problems.
If we want to live in more sustainable way, we could use this as an educational opportunity for our future engineers.
After upgrading to V5 many teams will be left with perfectly functioning components each of them having a high carbon cost of manufacturing. They already paid for them and recovered some costs (by using them with Cortex) - so those parts are, essentially, free for any secondary use.
I challenged some of our students to think about reuse cases that would make practical sense and would like to extend the challenge to anyone who might be interested.