Every time I have changed my Dac is to get something better. Not because I'm bored with what I have, a purchasing itch to scratch or a different flavour. I want to experience increasingly better sound.
Exactly. I've been through a number of DACs and all resulted in "better" sound to me, with "better" of course being subjective.
Whether something is "forever" or not depends a lot more on your listening tastes and budget than it does on the technology. DAC technology will continue to improve, but it's likely that those improvements will be small incremental ones and depending on your age and hearing, what you're more likely to hear is the "voicing" of the DAC, not its technical abilities.