This isn’t really a definitive trend though. Many older models are on 32mm (lesser daemons, savage orruks etc), and various new AOS models have been put on 25mm (kharadron privateers, tzeentch horrors etc)
So really I wouldn’t worry about the 25mm going away anytime soon. In fact, I really don’t see much evidence to substantiate this supposed ‘scale creep’. New duardin v old dwarfs are the same size, same thing with skaven, daemons, BoC and others. In terms of humans, we’ve only got one unaltered human to judge from, the discontinued silver tower war priest, though he was described as being a ‘monster of a man’ in lore iirc (he was larger than older human models).
The main difference I can see in AOS models are more spread out, dynamics poses, instead of actual size increases, which is simply a result of no longer needing to ‘rank up’.
Just my 2c.