eBay have given plenty of notice for developers to rewrite the code for their content (perhaps using HTML5 standards) and will provide more information later this year about which functionality will be limited and provide the specific timing in early 2017.
eBay are working closely with third party partners in cases where they use active content on your item descriptions.
eBay suggest that you remove active content today for faster load times of your listings, optimisation for mobile devices and importantly a more secure marketplace.
The security aspect is the most important. Historically sellers have used third party tools to add in functionality that eBay simply didn’t have. Sadly scammers use similar code for malicious purposes.
Today eBay have functionality to display images and eBay’s gallery works better for mobile display and for desktop search, they have cross promotion tools and there really shouldn’t be much need to add widgets to your listings. If you do want to then your widget creator will have to use modern code, not active content.