Is the problem to construct a $\mathcal{O}\mbox{*}(1.4^n)$ (or better) time algorithm for subset sum still open? I wanted to check the problem before finishing a paper.
The most recent reference I found to this open problem is on next paper:
'SETH-Based Lower Bounds for Subset Sum and Bicriteria Path, Amir Abboud et al.' 2017 link
citing:
'Open problems around exact algorithms, Woeginger' 2008 link.