Let me give you a concrete example; a hospital here in SF that is building a new facility has spent 30+ million dollars on coordination and constructability issues between all the trades.
There was far less printing of plans than there was hours spent coordinating the BIM model for changes.
Now, granted, this wasa project where there was an oversight in the design as it pertained to the owners intent and a number of critical technology spaces required were left out of the design.
This resulted in many hours of coordination efforts from all the trades to get these spaces into the facility, but a fraction of this was in printing.
If you can help with this problem, coordination, you have a much larger market.
The current industry trend is to err on the side of digital design and coordination meetings with IPD models, and reduce printing and field interference issues.
What might be an interesting opportunity for your service is to notify trades when changes occur that may affect them. THEN show them the new, updated PDF.
I don't know how this would occur -- other than the pushing of a constructability log or something....
Also, it would make sense that your app is much more focused on a the smaller project (HUGE market) of residential, smaller commercial etc..
Trying to force yourselves into solving the issues of massive scale projects may be suicide.