The UK has done this transition moderately successfully, albeit over 10-20 years. Not the AI bit, the amalgamating sites bit.

It had the opposite effect you're describing. Not quite everything has transitioned though, for example there are little bits of the limited company maintenance process that seems to be on old systems.

The only big hiccup that I've personally seen is that they've never really solved the "user id" problem, we seem to have had 3 different schemes in that time period. The early one, the government gateway id, I at one point had 3 different ids because some departments screwed up and issued you a new one the first time you used their service, when you already had one.