Adding...it appears that the feasibility to retrofit new functionality is also being phased out. I purchased my MYP last December (few weeks old), so I missed out on the new 12V battery, AMD chip, and all-season tires, among other things. Although purchasing an FSD in full covers future FSD hardware updates, it does not cover additional items that can only be obtained by upgrading to a newer model. Granted this could be supply chain related but reading the tea leaves - seems to be the direction.
In regard to Tesla trade-in. For transparency, the FSD value should be listed as a separate line item and not hidden in the offer. This also goes, with garage opener, acceleration boost add-on, etc. Tesla knows if you have them. If FSD is considered in trade in, show it with a competitive vehicle offer.
Last but not least, when it comes to subscriptions, offer the option of paying annually. It's mentally taxing to pay month after month for marginal progress. Although I am pro-FSD and like the process, justifying every month is difficult. Tesla, I'm sure, is under pressure to show results every month as well which could impact performance. This also helps owners who keep cars for a few years before trade in.