I think the double buses would work fine for most resorts, specifically for the Value resorts where I have seen the most complaints about double loading buses and long waits. Those resorts have large numbers of guests that they need to move all at the same time. I'm not positive, but I think that was where ost of the 'cattle transporter' type vehicles were being tried.
It could also work at the locations that share buses because the bus may be very full by the time it gets to the final resort.
I can see some diffuculty at OKW, because of the way the bus turnarounds are constructed. See the turnarounds near buildings 18 and 40 on the map.
http://www.wdwinfo.com/resortmaps/okwmap.htm
The regular buses are a challenge to fit there because the bus is very long compared to the size of the turnaround. There isn't room at OKW to change those, but some resorts with multiple stops have fairly straight stop locations are have space that they could rearrange them.