For all I know, Nokia is (and has been back then) a profit-oriented business company. As such they have a natural interest in their products to last at least the warranty period to keep their support costs low. After that they have an interest in selling new replacement products to the same customers. That's just how the market works.
There are different ways to achieve that and I will not speculate on which ones Nokia had in mind.

All I know is that they intentionally used software in their products that the user can't change and of which Nokia knew it would fail some day because the IT around them would change. That assessment is trivial, because anything else would mean to assume, that Nokia didn't know what they were doing, which I don't find realistic.

As a consequence it is logical to say the N900 is subject to planned obsolescence, because the (software-induced) obsolenscence is quite obvious and the planning is in the intentional design using proprietary blobs that does not allow end users to replace the OS while keeping all the functionality.

If the original maker releases all his work that is relevant for a specific project under a FLOSS license then anyone can pick it up and advance it. In this case it doesn't matter if the maker had any plans at all, let alone what they were.
I assume that anyone who is capable of making something is also capable of seeing that connection. So in my world anything that gets released without a FLOSS license is always subject to planned obsolescence, either by ignorance, incompetence or malice.

If you want to call that ideology, then I'm fine with it. I call it fairness.