Yes. Looking through K9’s blog, “recently” is more than two years.
K9 didn’t have a stable release for 3 years, until a previous contributor raised enough money to sponsor his work for a year or so. (Which I was happy to donate to, because K9 was starting to get really outdated UI-wise).
After that money ran out, they started working for MZLA Corp/Thunderbird more than two years ago.
They aren’t hiding the skip-button, they are hiding the not-being-able-to skip-button.
I guess the advantage for Google is that users can’t know whether they’ll be able to skip, so they might watch more of the ad with expectations that they might be able to skip it.