OK this might sound really crazy, but there is a kids sleep clinic where I work and what they do with cases of chronic insomnia with long periods of wakefulness like your DS is to shift bedtime later so that the child would sleep a solid stretch without waking up. I don't know how naps fit into this but I'd guess minimal naps to make sure the nights are OK. Once the child is sleeping well throughout the night for a few days the bedtime is gradually shifted earlier I think, but if the NWs start again then it is pushed back by 30 mins or so.
Of course there is the danger of OT creeping in but I think the main goal is to get the child going to bed at night and sleeping straight through until morning - even if it is only for 8 hours the first couple of nights. Then the nights gradually extend.
Not sure if it's too scary to try but I guess if you're desperate? So if he woke at 4am today, well maybe 1 hr nap and bed at 8 or 9pm? He will be shattered but hopefully would sleep through until morning. If it doesn't work, well at least you know you can rule that one out.
But I really think he is super low sleep needs, so I definitely wouldn't have any early pre-7pm bedtimes no matter what his day is like. To me it would seem his ideal routine would be something like 1 hr nap somewhere, bedtime 8-9pm with wake-up 10 hrs later. I know it's only 11 hours in the day but maybe that's all he needs?
I just see a cycle here - horrible day, good night to catch up and then the next day he is put to bed around 7pm and then has a long NW in the night. I really think it's because he's not that tired!
Actually read this in a book too, and it's something we are considering when Finn's a bit older. I see our future and this is it really.
Liz mentions the UT behaviour, Finn is the same after that 10 hour stretch he just sits in there, chatting, babbling, doing whatever, not really needing us but not really happy about being awake either. He's really been doing it since around 4-5 mths of age! But the problem is, if you leave them to it and he doesn't go back to sleep, what do you do with a kid that has been up since 4 a.m.? Our paed keeps telling us to leave him since he's not 'crying', yet if we do leave him he will just be up and eventually want some company. Sure we could try to go back to sleep and ignore him, but then when we do get up we have a hideously tired kid for the day. So is it worth it? I don't know. That's why I started the post on low sleep needs kids because I never know if I really have one or if it's truly just another UT/OT loop going on as has been since day 1. If he is truly low sleep needs then I have to try to work with that rather than forcing more sleep into him.
Sometimes I think you have to just do the total opposite of anything you have already done. If you are always thinking OT then think UT, think low sleep needs, and start to give him less sleep to see how he gets on. Come at it from a different angle.
I personally would give your no nap a try. You can always fall back to where you are now.