So with the Hawk Right wing of HP leaving and Koike totally marginalized with hints that she should leave HP, HP is now pretty much the DP Right of Sept 2017 which now is looking to form an alliance with DP (Upper House wing of Sept 2017 DP), and CDP (Left DP of Sept 2017 DP.)
Main problem for this CDP-DP-HP alliance if it gets formed in 2019 Upper House elections is how it can get JCP not to run in single member seats. If they can pull that off then 2019 Upper House elections could be competitive.
Easy solution to that problem: CDP shouldn't entertain such an alliance, and instead come to some agreement with the JCP.