Would there be a delay if you were running in a strictly HD-SDI master control switcher using master control automation software?
There can be if the automation software has to figure in pre-cue delays for various bits of kit. The delays may be smaller - but they still exist.
But moving forward HD-SDI is an increasingly legacy technology, so won't be with us for that much longer I suspect. Playout is ahead of the game in moving to all-IP paths, but production is following.
(Though Quad 12G and the new fibre-based U-SDI standard are finding use in 8K Production, where baseband bitrates make IP less compelling in the short term...)