I get that building a _new_ automated metro is easy. Converting an _older_ line to automatic and fully driverless is what's hard. AFAIK, there's only one conversion so far to full auto: Line 1 in Paris. It took 10 years and billions of euro to deliver (it's a total success though) https://en.wikipedia.org/wiki/Paris_Métro_Line_1#Automation

Interestingly, it seems the main obstacle is software - contractors are few, code is highly specific, ISO certification and warranty issues are very unattractive.

Very interested how TfL will approach this. They're really good at what they do, even at communicating (responsive website!). Don't think anybody does it better.