A teacher of English from Hong Kong writes with a grammatical question. 'I have spent many years teaching students the difference between stative and dynamic verbs and telling them they can't use stative ones in the continuous. However, I'm quite delighted to hear that you obviously can, as so many native speakers are now doing so. Thus I'm hearing (you see!) 'I'm not believing you.', 'I'm not understanding.', 'I'm liking it.' as well as the ubiquitous 'I'm loving it.' This seems a very positive change which I shall teach my students. To me 'I'm not understanding.' implies 'I might understand if you keep trying to explain.' 'I'm not believing you.' 'Keep trying and I might.' 'I'm loving it.' 'Whatever 'it' is is not of permanent concern to me.' I have two questions: Is this a permanent change and, if so, when are teaching materials going to catch up with it?'
Many grammarians (see, for example, the big Quirk grammar) emphasize that stative and dynamic are best viewed not as two types of verb but rather as two potential uses of a verb - much as countable and uncountable nouns are best viewed as two uses of nouns, in view of examples like 'some cake vs a cake. The idea is that the norm is for verbs to be used in both ways, with the appropriate change in aspectual meaning taking place. Those which disallow one use or the other are then seen as the exceptions, such as *I'm owning three cars.
Why is this sentence odd? As your examples illustrate, the sense expressed by the continuous form is one of 'activity in progress', and as own is a notion which doesn't have any sense of progress, it would be contradictory to use a grammatical form which suggests that it does. The meaning of the verb has got to allow a dynamic meaning before it can be exploited in this way.
You have to watch the grammatical context, of course. While it is perfectly possible to say I'm liking it, you can't do so with a clause complement (*I'm liking to visit libraries). So it's important not to give students the impression that they can use continuous forms willy-nilly. Having said that, some varieties of English (especially Indian English) have long been distinctive in the extent to which they use continuous forms, even in contexts which would be ungrammatical in British English.
The usage is by no means new. It seems to have grown in frequency during the early Modern English period. Very early usages include Jane Austen 'it was being very deficient' (in Emma, 1816) and Keats 'I was not existing' (1820), and the usage seems to have become more widespread during the 19th century and after. There's a nice discussion in the essay by David Denison in the Cambridge History of the English Language, Vol 4, p. 143ff.
I can answer your first question: It's definitely a permanent change (for the forseeble future, at any rate). But how long it takes for teaching materials to reflect such changes is well beyond my ken.