The technology isn’t really a problem. The units themselves could probably be made to fit in an iMac without too much trouble.
The problem is the numbers of parts their suppliers can make at a particular time. They had limits on how much they can keep making. So if then they have to prioritise what devices they use them for. They will likely decide that they need them for other iPhones (because iPhones make up most of their revenue), and then iPads because they need to differentiate new iPad Pros from the recent iPads that are aimed at education (because those have pencil support now).
Macs will be lower on the priority list because going to 6-cores on the 15” MBP & 27” iMac, 4-cores on the 13” MBP and 21” iMac is enough to encourage people to want a newer model this year.
The problem is the numbers of parts their suppliers can make at a particular time. They had limits on how much they can keep making. So if then they have to prioritise what devices they use them for. They will likely decide that they need them for other iPhones (because iPhones make up most of their revenue), and then iPads because they need to differentiate new iPad Pros from the recent iPads that are aimed at education (because those have pencil support now).
Macs will be lower on the priority list because going to 6-cores on the 15” MBP & 27” iMac, 4-cores on the 13” MBP and 21” iMac is enough to encourage people to want a newer model this year.