Getting Seats on BMI Codeshare
 

I am on a UA Codeshare on BMI metal and do not have seat assignments. I imagine I will be in a middle seat somewhere in the back regardless, but any idea on how I can try to get a seat?

Also--and I am pretty sure the answer is no--with the way the ticket is structured (LAX-LHR in V and LHR-AMS-ORD-LAX in B), does my one-way upgrade (15000 miles) also apply to all segments or just those on UA metal?

Have you tried calling BD directly? It doesn't matter that it's a UA codeshare, you are in their reservation system and they can assign you a seat if you call them directly.

Only to UA segments... you cannot upgrade on non-UA metal on the same reward. Not that it matters... really no big difference between C & Y on these flights.

If I was going IAD-LHR (overnight of course) and then connecting to BD. Will UA be able to print out boarding passes for the BD segments?

Yeah, UA can check you in for the BD flight the next day.

I mostly fly LHR-BRU on BD and there is barely ever anyone on the plane. I assume the same goes for your flight so, I wouldn't worry too much about seat assignments on this one since most people just pick whatever seat they like, once on board :)