I've been working on a blade fuse retrofit kit for e28 fuse boxes for a number of months now and it's high time I made my own thread about it. I'm very close to a final version and will be posting updates here as progress is made.
I'd like to thank @cek for offering up his cars as guinea pigs - his input has been invaluable for improving the final product.
Quick specs:
Compatible with standard / mini / low-profile blade fuses
Works with both Euro and US cars
Lower total resistance and won't lose spring pressure over time
Indicator LEDs to identify blown fuses
Does require modifying the fuse box by removing the bullet fuse holders, but drops into the existing slots through the plastic
Fits under the stock fuse box cover
Here's a photo of the current prototype:

See the installation here.
Let me know if you have any questions.
-Galahad