Re: Diacetyl, I agree totally, Vego. For anyone who is concerned about acetyl/acetoin, you can always get TFA's Vanilla Swirl, which contains neither and is quite a reasonable substitute for any VC flavoring I've tried.
And yeah, I'm subscribed to this thread so I can follow the progress here! I'm a huge vanilla fan and probably would never have gotten into DIY to begin with if I could've found a pre-made vanilla juice that satisfied me. Not so much a huge fan of custard, per se, but I'm definitely going to be trying out some of these variations in the near future!
My own vanilla concoction is a mix of 12% Hangsen Vanilla, 3% VZ Bavarian Cream, 2% TFA Malted Milk, and 1% sucralose in a 70/30 10mg base. I've been quite impressed with the Hangsen Vanilla, which seems to have a creamier feel/flavor than other French Vanilla-type flavorings I've tried. After a 2-week steep, it's a pretty sweet and intense "in-your-face" vanilla flavor, not unlike vanilla taffy. I think it'll be better with a higher VG content to cut the flavor and improve mouthfeel a bit. Still experimenting...