Matt Wheeler wrote:

I'm sure they do understand, hence the replacement bus service, and
the publicity of the works. Since Terminal 5 is happening, how would
you propose extending the Picadilly line to that terminal without an
enforced closure of parts of the line. Or would you rather the
Terminal 5 passengers (when complete) are inconvenienced by poor rail
links when it opens, just so people wanting Terminal 4 aren't
inconvenienced now.

What would you propose to do ?

As was done during the building and extending of every deep tube line on the
underground since the 1920s. Build the junction round the existing tunnel
whilst allowing the service to continue running.