First, I'll try to understand the motivation behind the move. Storage is an expense. Hence wanting to reduce size is obvious. However, is there any particular type of user that we want to reduce the size for? Is there any particular type of files/data that we want to focus on reducing? Are there any trends in accounts requiring large storage space?
Assuming the goal is to reduce overall storage size, I can think of the following options:
- File compression - tradeoffs are usually increased latency and sometimes loss of quality
- Dedupe - In all probability this is already being done but explore any possible optimization of deduplication algorithm
- Limit the size of individual emails - this would encourage users to not use gmail to send emails with large attachments such as media files. Users can switch to paid accounts for Google drive for sharing/sending large files.
- Archiving old emails - emails and attachments that are not accessed often or recently can be archived to cheaper hard drives
- Anti-spam tools - This is a win-win for both google and its users
- Better targeted ads/referral programs - Ways to offset cost by increasing revenue generated per gigabyte of storage space. Serving more relevant ads will improve user experience and help google command a higher CPM. Referral programs may be a way to increase user base and thus reach of ads placed on gmail.
Of these options I think #s 4, 5 and 6 have the most bang for the buck with least impact to user experience. 5 and 6 will require high initial investment but will pay-off in the long run.