Google recently announced that any page that has a form asking for payment details or has a password field in it will be marked in their Chrome browser as not secure, starting January 1st 2017. See: -

Google Online Security Blog - Moving towards a more secure web
Come in HTTP, your time is up
Chrome to Label Some HTTP Sites ‘Not Secure’ in 2017

Many MDD member sites have customer login sections. If this is through DJEP they're usually framed, I think, and so might be OK, but I've seen others that use their own forms and those really need to think about installing SSLs to enable HTTPS.

Also, anything requiring Geo-location now requires HTTPS. This probably has less of an impact, unless you're trying to determine where the visitor is, of course.

One plus is that if you do jump to HTTPS, you can then add a payment form (using, for example, Stripe, who insist on an SSL) relatively easily.