I think you'd then have to enter some kind of a lease agreement, which would be a big turn-off for customers that would like to just buy a replacement cartridge without signing a contract.
1) As with many of the tricks that printer companies use to dissuade people from buying off-brand inks, if enough printer manufacturers did it, consumers might find that they have few other options -- especially if they've had poor luck with third-party inks.
2) I pay $3 a month for HP's Instant Ink program. It allows me to print up to 50 full-color pages a month with my inkjet printer, and when one of the cartridges is running low, it automatically sends a replacement. It's not significantly more expensive, in my case (low-volume usage), than buying the ink cartridges directly, but it's a lot more convenient. I'm not quite sure if it technically counts as a leasing program, but it follows a similar ethos. So I wouldn't so easily dismiss the idea that a leasing program would lead to a consumer backlash.
