To my knowledge last SUPEE update was in March/April 2016. Any ideas when to be prepared for another SUPEE update for 1.x versions?
The disclosure of potential security exploits to Magento platforms is not publicly available. If it were, you'd just see floods of exploits hitting your site whenever one was reported.
As such, you're not going to be made aware of fixes for these exploits until they're physically released to the market in the form of a SUPEE patch.
Essentially, no - it's unlikely you'll be able to find out when security patches will be released. Just follow the Magento security listing pages and keep an eye out.