What 'makes you guess that', is it it the fact that the same thing happens with every new GPU upgrade cycle since the last decade(s)? Mind blown at your levels of premonition.
Jokes aside, if supply of the RTX5090 is really restricted at launch like happened last cycle, then after the initial rush it may be that 4090's maintain more value as it's all people can get for a few months until 5090 comes back.