Hi there kdewolde, it sounds to me like he's gone from one extreme to the other; having quite a lot of daytime sleep and a long NW, to now drastically less daytime sleep and still a NW. Was there any time in between when he didn't have the NW? Did you not have luck with a morning CN and a longer afternoon nap? One last thing, do you think he's dependent on the soother to go to sleep? Does he know how to replug himself?
I think he's now OT, actually. A 12 hr day is great, but really quite long for only a 1.5 hr nap at 10 mo. Ideally at the beginning of one nap, you'd like the nap to be 2-2.5 hr in length with an 11-12 hr night. What seems to have happened is that the nap is long enough for him to not really be tired enough for another nap in the day, but it's ending pretty early in order to make it to bedtime. This is a scenario that lots of LOs run into during the 2-1 transition.
You've got a couple options to try. The easiest at this point would probably to start pushing that one nap out by however much he can handle every few days. So, add 10-15 min of A time and hopefully the nap will lengthen. It may take a few days, but hopefully it'll start to get a little longer. After a week or so, you can add another 10-15 min and wait for it to lengthen again. The goal being that you want to get that nap into the middle of the day, so he doesn't have such a long A time to bed, which usually causes OT on one nap. Until you get that nap to where you want it in the day, bedtime needs to come back. I'd do it at no later than 6:30 pm. Most LOs will do a longer night to catch up from lack of day sleep and make it all the way or near to their usual wake-up time. This should help the NWs as well.
The other option would be to go back to trying the morning CN and longer pm nap, so that he's not going to bed OT. This would take a bit of tweaking at this point, since he's used to that longer nap late morning, but can still work if you want to try it. It might not be a good idea to cut from 1.5 hr to 30 min all in one go. You could start by cutting to one hour for a few days and then back again. The day (eventually) might look something like this:
W and E 7:30 am
Nap 1 11:30-12:00 pm
Nap 2 2:30/3-4:30 pm
BT 7:30/8 pm
What do you think?