Is there such a thing as a FOREVER DAC/streamer?

No such thing really. 
however, some have firmware updates. 
Take the Lumin (I have a D2)… since I purchased, there have been several updates. 
it’s part of their DNA to continue the updates. For my non-vinyl purposes, this is possible my last streamer purchase. 
 

the PS Audio airLens looks quite interesting, however. 

+1@jeffreyw

Check out Aries Cerat

My DAC is my most expensive component, a PS Audio Directstream w/ streamer card. And I’m glad because streaming is more and more of my listening. It’s software-based, and they’ve issued a number of updates that are easy to make with just an SD card. But still … now they’re introducing a new version and will stop upgrades to the Directstream. So I suppose there’s no such thing as forever in digital. But I do think this source is so important that I’d still spend what it takes to get a great one.

@ghdprentice 

At some stage, you're right that components may end being the last upgrade.

I'm working towards that myself. Have speakers, DDC, Dac, streamer, RCAs, power cables, digital cable, speaker cables sorted.

If no chance to upgrade LPS, external clock and amp, I'm fine with what I've got, and fine with the sound. Having been in this game for 46 years, I know I want to upgrade those as well.

Almost every product promising a “future proof “ platform is forced into obsolescence by technology and or OS / Hardware limitations 

When technology is a constantly moving target there is no such thing as being future proof.