As digital media go, email isn't typically exalted for its cutting-edge progressiveness. It is constantly evolving, with increasing analytic capacity, data integration and other functionality. But it doesn't seem to follow the same digital media trends making the rounds in Online Media Daily, the Social Media Insider or even the Mobile Insider newsletters. So far, it hasn't needed to. Email doesn't need to rely on sexy, as long as it can rest comfortably on its ROI and marketing department ubiquity. You know what they say about the winds of change, though -- they blow. As the landscape shifts, it's becoming clear that engagement will become critically important to email marketing -- not just to boost ROI, but because of its growing importance to deliverability and sender reputation. I believe some of the biggest innovations we will see in the industry in the coming years (or even months) will be designed to boost engagement, since the benefits greater engagement yield can impact an profoundly affect an organization's email program Here are a few innovations I've been thinking about, that in past years haven't been worth the investment. But with engagement at a premium, we may start to see more energy and resources devoted to tools previously considered pie-in-the-sky, but now looking a lot like the cost of doing business: 1. Survey-based targeting. Behavioral targeting in email has long existed: if you email your previous customers specifically based on past purchases, you're in the BT business. But BT is limited to assumptions based on observable data, making it susceptible to false negatives and false positives. For example, Dave might really want that KaPow oversized driver featured in today's message, but his birthday is next week and his wife has already promised it to him. Dave has no reason to click through the email, much less buy it. Still, a sender could conclude he doesn't like the driver, or KaPow, or golf altogether -- each of which is a false negative. As it turns out, Dave's wife shops at the same online retailer and decided to purchase the KaPow driver for him there. She knows nothing about the product, brand or sport, but Dave did write down for her the exact name and model to make her gift-giving easier. She buys him the driver, which Dave loves so much that he throws himself headlong into the game, sacrificing every weekend to 36-hole marathons and every available week night to the driving range. Dave's wife leaves him, of course, but still receives an email at least once a month featuring other KaPow products and equipment from other golf companies. She's a false positive. Survey-based targeting relies instead on explicit input from consumers, combined with observable data, to create consumer profiles used to anticipate behavior or identify attitudes or values that drive behavior. The survey component requires the use of panels, since only a small percentage of consumers will participate. But a large enough sample size (more easily achieved with a population of subscribers who already have a relationship with the sender) would allow an email marketer to extrapolate, and identify the segments the subscribers in the much larger group of survey non-participants likely belong in. As the size and data richness of house lists grow, segmentations like this become more feasible. 2. Collaborative filtering that treats messages like products. Amazon.com pioneered collaborative filtering at the product level, allowing the retailer to make cogent suggestions for products a shopper might like based on her past purchases and the purchasing history of other shoppers who bought some of the same items. The premise is that not all shoppers can survey the entire available inventory and spot something they like. Collaborative filtering amounts to some helpful editing. But in our world, the same problem exists. Our subscribers miss or ignore messages when they are distracted or away, even if the messages are well-targeted and the subscriber would genuinely be interested in the content. Imagine treating your messages like products and giving subscribers who overlooked them another crack. At the bottom of this week's offer, a sender might have a list of recent offers well-targeted to the subscriber, but ignored the first time around. "If you like today's offer, you might also like these." The links go to the Web versions of the past messages for that subscriber, complete with tracking. 3. Paid premium email subscriptions. "This is the only piece of mail worth keeping," I said to my wife yesterday evening when I was sorting the mail. Three catalogs, two credit card offers, three account statements (viewed regularly online), four postcards from local businesses and one fundraising request from an environmental nonprofit all went straight into the paper recycling. The only piece to escape the daily purge was the bright red Netflix envelope containing the DVD that is part of our monthly subscription -- our paid monthly subscription. Paid content isn't new online, but what exists today are paid subscriptions designed to monetize premium content. I think we are not far off from paid versions of very high value email. For example, appointment shopping sites with limited offerings like Gilt or TheClymb might get away with a premium (paid) subscription giving subscribers early access to select deals. Groupon, LivingSocial and their ilk could do the same for partners with limited availability - like a restaurant opening or a book-signing event. And retailers, travel sites and others might all have an opportunity to craft a new premium subscription with exclusive offers. If a few million people will pay 99 cents to download "FatBooth" onto their iPhones, surely there must be a market for paid email subscriptions that promise the subscriber savings many times over the purchase price. The rationale behind these subscriptions, however, would not be to drive revenue; rather, it would be to cement engagement. As with my red Netflix envelope, people will pay more attention to what they have paid for. As engagement metrics influence sender reputation, hyper-engaged programs can boost the effectiveness of a sender's entire program. With engagement at a premium and email remaining mission-critical to marketers, the scope of possible innovations is vast. What do you see coming down the pike? Maybe more interestingly, what do you see coming behind what you see coming down the pike?