The Rev E is still on the back burner, though I need to address it sooner than later. Basically I had started the changes to incorporate the EFB mod, but then stopped it as I wasn't happy with the layout and the changes required for individual biasing. Just two months ago, I revisited the ST35 Rev E and experimented with 1% zener diodes in the biasing circuit in a very similar scheme as the current design. So I think I will go that route so that the board can do the regular resistor scheme or the zener bias scheme (whose dynamic impedance is much lower than the biasing resistors).
I have an urge to build an ST-35 and since I have quite a few 12AX7's and 12AU7's the diytube version is my first choice, but I can't see using the Rev. C boards and kludging the EFB on it (although I would probably kludge EFB on a Rev. D). So it's either wait for Rev. E or use the original Dynaco boards.