They've been caught in the past slowing down old iPhones claiming it was to preserve battery health. I think claiming they definitely will do it is a bit much, but it seems plausible enough.

Reality

It's not a conspiracy, Apple (and many other companies) has been known to create software updates meant to slow down older devices to encourage users to upgrade.

When apple is involved, usually history. They've done it before. It's not unreasonable to expect it to happen again. Especially since apple themselves are surprised at the popularity of that device. Once they heeleits eating into air and pro purchases, things are likely to change for the neo.