"They could just allow Play to be installed, then let people choose to download the rest."
You mean like this?
"This package is designed for users who want the absolute minimum GApps installation available. In this package you will find the core Google system base, Google Android Shared Services, Google Play Store, Google Calendar Sync, Dialer Framework and the following Play Store applications:
Google Package Installer (replaces stock/AOSP Package Installer)
Google Play services
For 6.0 also: