I replied to a question someone had & it got me thinking about how I'd like to see Marketo solve subscriptions. Here's the thread -
https://community.marketo.com/marketodiscussiondetail?id=90650000000PuCsAAKIn Admin where you create new Tags I'd like to be able to create a 'special' Subscription Tag. Here you could create tag values for each type of email you send. Whether that's by product 1, 2 & 3 - or - newsletter, content, promotions. This would (naturally) sync with a special Subscription Form Field. These values would be in sync with subscription preferences - only changed in admin.
It would then be the marketeer's responsibility to tag each email they create with their Subscription. Since you can require this be mandatory it's easy to inforce compliance. Then Email programs, Engagement Programs & the Schedule Tab of Smart Campaigns would all understand & respect that anyone who had restricted that Subscription would be blocked from emailings.
This would be a huge win to have a streamlined & easily managed process.