I wouldn’t downgrade to V1, since you might use plugins wich are only supported for v3.
People will adapt to newer Phones anyway. Since most of their apps they are using won’t be able to run on their platforms anymore. Don’t worry to much about losing a customer.
What you could do is you bring out 2 versions to the Playstore one wich runs on the older devices and one for the newer ones. The downside is that you will have to patch 2 versions all the time and you have to know the old version of angular and the new one ofc, much more work for you etc…
In your case I would stay with Ionic 3. Like I said your customers will adapt since they are using many more applications wich they love and use on a daily base. If their Android version won’t be patched anymore they most likely buy a new one.