When any random company makes a Build vs. Buy decision the question is “is this a core competency?” Most companies use a package from MS or GOOG because it’s unlikely that they’ll be so good at productivity software that it’s (A) worth distracting themselves from their actual job and (B) good enough. The same caveats apply here.

so likely a decade or more of double spending in the meanwhile.

that's 2 election terms in France for context. Good luck making the political parties agree to this.