I don't quite like the new design of the play store, and wish to stay with version 3 of it.
Is it possible (by root if needed, and I think it is needed) to disable it from auto-updating?
Will I even miss anything from the new versions ?
For now, the only solution I've come up with is to use the really old 2.3.6 version of the market app.
This is the only one that doesn't auto-update itself.
In order to install it, you have to uninstall the play store, install it, and convert it to a system app.
If you wish, you can use titanium backup to backup the old version for later use.
The only way I've been able to do it is with Lucky Patcher. It has a "custom patch" for the play store that disables the self updating. It may not work with all versions but it worked for me running 4.9.13