Looking on the Intel website, it looks like the latest 32-bit atom processor they released was in 2011 and is already end of life. The last still supported were launched in 2010 [1]. All new intel processors (Joule/Curie etc) are 64-bit architectures.
Regarding statistics, Debian saw amd64 taking over i386 around mid 2012 and today there is a 3.6:1 ratio [2]. For ROS packages, amd64 downloads exceeded i386 since 2015, last month’s statistics of xenial downloads show amd64 packages downloaded ~20% more than i386 [3]. We do suspect that most i386 downloads are made for computers supporting 64-bit instruction set but running x86 OSs
It would be interesting to see how many people among the community are actually installing ROS on 32-bit processors to make an educated decision.
[1] https://ark.intel.com/fr/search/advanced?s=t&FamilyText=Intel®%20Atom™%20Processor&InstructionSet=32-bit
[2] http://popcon.debian.org/
[3] https://awstats.osuosl.org/reports/packages.ros.org/2016/12/awstats.packages.ros.org.urldetail.html