I've used Qt in professional environments with commercial licensing at previous gigs. I'd considered using Qt for personal projects using their open source licensing. But this is a killer requirement. Goodbye, Qt.
"Download the open source version if you're sure you can comply with the LGPL" is just a threat, pure and simple.
Thus, I wouldn't touch Qt in a commercial venture that is too small to have full time legal counsel on hand.
5500/year/developer is significant just about everywhere outside Silicon Valley.
[Editing comment because we're over HN's threading limits] @avamander:
But who decides that I've complied with the LGPL? Do you think it's as simple as dynamically linking with their provided binaries and making public any patches to Qt? I don't think so. It smells to me that if they decide you owe them money, there'll be a lawsuit coming.
Additionally, trying to compile the project from source is extremely painful compared to most projects: it's not really possible in any obvious way to duplicate the output of the binary distribution without looking at the guts of Qt's continuous integration environment for weeks on end.