Uninstalling (or going back, if you prefer) will always be subject to the Play Store update. Yiu cangio back, until the store sees you hav e an outdated version, and it will always be there, you cant get rid of Play Store nags.
Yes, try some of the other keyboards suggested, but the stock will always be there and you will always be pushed to update it if it is old.
TLDR:
The main reason why N will tackle the "Disabled " option much better than Marshmallow does. As many have found, when you want to Disable a stock "bloat" app, you can, but before it goes to Disabled mode, it has to uninstall any and all updates that had been applied up to that point, and brings you back to the stock app, but now disabled. You cannot disable an app at its most current version. No reason behind it, you just cant do it. Then of course, once an old app is Disabled, the Play Store will see the old version and force nag in the Store until you update it. Once you do (if you decide, and it is the only way to remove the Store nag), the reupdated app immediately becomes re-Enabled. Thus making the Disable "feature" useless, and pointless. N is supposed to fix that issue. It is not known if the app will remain Disabled in its most updated state be pre-reverted to its original stock state, before Disabling holds.