It's said we'll have five to ten years until the old TVs are landfill. I wouldn't be surprised if they last much longer, though. Because a new technology seldom completely obliterates an old one. People still swap 8-track tapes, still buy vinyl records, and still use buggy whips. The buggier people, that is.
Old technology has a tendency to hang around for some time when a new one shows up.
Often the two co-exist indefinitely. That's something to remember when people speculate about what new technology will supplant the last, whether the 1.4meg floppy will be replaced by the 100meg Zip drive or some future interstellar storage technology. Heck, I expect even humans will be around for some time. At least until the weekend. So, in all the speculation over what new technology will become the current standard, remember some people still wear double knits.