Don't quote me on this though, because I wasn't a first party member of the conversations.
RAD (rapid application development) of GUI applications was never easier and such a joy then with VB6. I remember I was very sad when they announced their vision for dotNet - it took them additional four years until dotNet was available in v1. In the meantime they lost all developers to HTML and PHP & co. Dreamweaver WYSIWYG was good enough.
But for people who have to support VB6 regardless of whether or not Microsoft open sources it, I'm sure it'd be pretty helpful.
We still have stuff out there that runs on COBOL, I have a feeling there will still be some life-dependent VB6 code out there somewhere in 2050.
Thinking about it, I am going to dig out my old VB6 VM image and have a play. Be interesting to see how many people out there would want support for VB6 apps today.
Said it before and I'll say it again, I don't think there is anything out there now that was a productive as VB6 development. Rapid Application Development was the buzzword of the day, and it really stood up to the name.