Its not so much as being forced to use SSL ( yet ), but the user experience will be hindered somewhat which isn't the impression you'd want to give new users nor is it good if your APP is being indexed as its highly likely it will be affected as a result of the changes coming up through next year. It makes much more sense to get rid of Tapatalk if the forum isn't planning on switching to SSL for a while yet.
With SSL most likely being forced for native apps at some point in 2017, I'd highly recommend any forum to move to HTTPS after careful consideration OR starting to ease your users reliability of Tapatalk, especially on forums such as this where Tapatalk usage is minimal and unlikely to cause any significant user unrest.
Moving to SSL isn't a straight forward of a decision that should be taken lightly and a 3rd party app with minimal usage certainly shouldn't be the defining factor on a decision. For many sites revenue and traffic deterioration is a huge risk even when taking all precautions, the severity depends on the niche and if your core revenue is generated by particular ad networks, some sites see up to a 60% decrease in revenue while improving or retaining the same traffic levels and retention stats. As you can imagine for many sites a 60% drop in revenue isnt viable or sustainable.
Tapatalk is a liability and has been for years. The majority of admins will be glad to use this as an excuse to jump ship and bring users back to using their own platform instead of a 3rd party you have no control over. Take back your mobile users while you can.
SSL will play a massive part in all sites over the coming 18 months, any site should be considering it and planning for it. But none should be asking "how high" when a 3rd party like Tapatalk says "jump".