I had a plumber in a couple of weeks ago and he said it would be a big job...lifting some floor boards, putting in a new motor valve to zone off the upstairs rads etc (I'm hopefully phrasing him correctly here). So I left it and just went with other work I had him in for
It really depends on your existing setup. I decided to separate zones when I had to get a new boiler. It turned out that the existing plumbing supported zoning - I had valves in the hot press that I could manually turn off for example if I wanted radiators all off but continue to heat water.
The plumber was able to replace these with motorised valves. There was a lot of cables to run, but it didn't need additional plumbing work, or ripping up floorboards.