Would you mind sharing more details about why you think it's going to be painful for seniors to adjust? The answer might be obvious, but I'd love to hear more about the difficulties that you've faced teaching seniors.
I don't teach seniors per se, so I can't answer "professionally" but I have taught two of my grandparents how to use their phones (one old Motorolla flip phone, one on my old iPhone) and computers.
I found that they were very hesitant to engage with the phones, they have a preconceived notion that touching the wrong thing could break the entire device (which is generally an incorrect assumption but not completely).
The way to get around that fear, of course, is to make sure all the steps are followed in order in the way they were taught, eg: To Make a Phone Call: 1. Press the green icon with the phone on it at the bottom left 2. Press the picture of the star to bring up your favourites 3. Press on the name you want to call. 4. When you're finished, press the big red button.
In that example the four steps are largely unchanged, and every identifiable interactive element (green icon with phone, star, names, red button) has the same general description.
But everything has changed slightly - the green icon isn't the same colour, the star is a bit different, the names now have photos next to them and the red button is a big red strip.
This isn't a big deal for you or me, but it is certainly a big deal when they're looking for the clues in the interface that they are used to.
But things like "Slide the grey button to the right to unlock the phone" and "slide the green button to the right to answer the call" have changed significantly. There's no more grey or green box - there's no box to unlock and the green box is now a big green line.
My grandfather is doing pretty well with his iPhone by muscle memory, but he literally has a piece of paper in his phone case with all the steps written down in order so he can refer to them if he gets stuck.
Changes on this scale break the muscle memory that they've been trained to use, but more importantly makes the steps he's been taught incorrect. It's no small feat to have to learn everything over again. Especially so when things aren't brand new anymore and the changes are only slight.
