FWIW some tools including an official one from Google exist to help in migration. I've worked with both 1.3-1.5 as well as 2, 4 and 5 and if I inherited a 1.x

FWIW some tools including an official one from Google exist to help in migration. I've worked with both 1.3-1.5 as well as 2, 4 and 5 and if I inherited a 1.x codebase I'd rewrite it, if necessary one piece at the time.