This is not a compelling argument. I'm not going to stop using a powersaw to cut beams just because another contractor refuses to use anything but his handsaw.
Besides, reading implicit types has _never_ been an issue on any team or collaboration effort in the 30 years of my programming experience and I find it _really_ hard to believe anyone that claims it is a bonified problem for readability. In fact the complete opposite is true for me, personally, that too much information in front of me becomes noise and the signal gets lost.
"bonified" is a particularly satisfying bone apple tea
yeah I've no idea why I spelled it that way.
They're not talking about someone using a hand-saw, they're talking about someone using a powersaw from a different manufacturer. Or, y'know, a table saw, or a CNC machine. Kotlin has tight integration with one particular IDE, not with all IDEs; let alone with things that are powerful in ways orthogonal to the ways IDEs are powerful, e.g. Emacs.
Eclipse has feature-parity with IntelliJ in this space, it just has questionable usability and performance.
Considering that many people willingly work with languages like Python and JavaScript, which make ANY IDE/Editors job of completion horribly difficult, the worst case is you end up with an editing experience on par with other languages.
So long as everyone on your team uses IntelliJ, then no problems. But not everyone uses IntelliJ, and now you've written code that is only easy to parse in a particular IDE...
For this reason, and being able to read my own code outside of just my IDE (say, in Github, etc), I've found it more necessary to be explicit with my typing in Kotlin for all but the most trivial snippets.