Speaking just for myself...I like that Slack has the same look and feel no matter what platform I bring it up on. I prefer a unified cross-platform experience over a unified platform experience. I want my OS to disappear. I am probably biased by regularly targeting multi platform myself.
This causes me to favor other lowest common denominator idioms as well, like python 2.7 over 3, unconfigured vim, bash on windows, etc. When this isn’t possible, I favor technologies that allow me to synchronize configurations across platforms quickly and easily.
This will hopefully appease the electron haters but I suspect someone will still complain about this being JavaScript