This is the main reason I dropped my Ubuntu PPA, because there is no easy way to build QupZilla there. Please don't use it anymore, I also removed it from homepage.
EDIT: Looks like QtWebEngine made it into Debian Sid repository just after publishing this blog post. In any case, it will still take at least about a year until it gets into stable Debian/Ubuntu release.
How to get latest QupZilla on Debian
Your only option currently is to build it yourself. For this, you need to use Qt version that comes with QtWebEngine (eg. offical builds or from PPA). After that, just proceed with build instructions as usual.
However, this is far from ideal. Recently, there have been efforts to get QupZilla build and run as a universal Linux package (snap, flatpak), none of them are unfortunately in usable state yet. In any case, I believe this is the solution for the Debian issue (and will be useful for other distributions too), and I hope remaining issues will be sorted out soon.
What's coming in QupZilla 2.1
I have also been working on a new version of QupZilla. It is scheduled to be released when Qt 5.8 is out. One of the features that is coming back is spell checking.
|Current Spell Check Preferences (work in progress)|
Qt 5.8 is currently scheduled to be released on 5th January 2017, so that also means new QupZilla version won't be released in this year.
That's all for this year, I wish you all Merry Christmas and Happy New Year!