I was thinking somewhat along the same lines

Recently read Resilient Web Design, got inspired and told our UX designers in our requirements docs we want mobile first

Then we get into check in meetings and I’m seeing desktop layouts and I’m like wtf guys

My partner (dev) is like yo let’s just roll with it I can make this mobile later… and this will be faster/cheaper

So I compromise and say fine but as we do this I want to be able to understand clearly how this fits on mobile in the future.

And it’s reasonable… the issue keeps coming up (i.e. I keep asking) and if there’s no obvious solution we change something to acknowledge future mobile

…But at the end of the day we’re now making a web app first with desktop layouts lol 😩