Per NEC the future for the IPK II is at least 10 years. If for any reason anyone with the current platform wanted to upgrade due to advance features will very little expense.

New phones are modular. If you bought a 6 button phone and in 1 year you decided a 12 button is needed instead of buying a whole new phone you buy a 6 button kit, you remove a blank cover on the phone and the button kit slides in and presto you now have the 12 button phone. The same will work with 3 different displays, the largest being touch sensitive.
Decided you need a cordless, slide off the handset cradle from the main phone and slide in the cordless base unit.

I will have to look into what the UM512 is, top of my head I don't know, I will find out.

We get old too soon, smart too late