For real. It's hard to imagine somebody so fulfilled in their lives that the only way to move the needle is to go somewhere with that perfect tech stack.

And not taking the job isn't even the best way to solve that problem. I'd ask them how married they were to CS and if moving off of it was doable.

If the shop is reasonable they won't have any objections so long as you're not hurting delivery targets to pursue your pet project. If they're not reasonable then you've found out a very important fact about that shop and that in itself can be a deal breaker.

I talked myself out of a job offer once when I stated that my main motivation for jumping was to work on a more well-maintained codebase. Kinda glad I did, but it was a wake-up call. If I'd tried to pull that shit when I didn't already have a great job, that would've sucked.