i would like to note that i havent played the latest industrial craft or build craft (let alone together) however after watching videos and knowing things from the past, i see some opertunity for a bit of bridgeing that can be done
first off, you could add an electric engine, it would power buildcraft items such as quaries or fillers, but would itself be powered by minecrafts electricty system, perhaps the electric engine runs faster the more power you send to it, so a current of 5eu would produce the same as say, a buildcraft stone engine, but if you send it 10eu it does the same as an iron engine, or 30eu and it would be like 3 iron engines
it might explode ofcorse if you overload it, say at 50 eu
second, buildcraft now has oil, perhaps you could add an oil burning generator to produce EUs for your minecraft system
im sure there are other possibilities for bridgeing these two great mods which just beg to be used together, but these are the things that come to mind