Um, does he way over-think things like you? JUST JOKING!!! :) I understand everything you said, and I am also not a playdater. I suppose you would just have a casual environment at your house to have a mom come hang out while the kids play. Just be nice, gracious and relaxed, like a friend is coming over. (cringe-like I said, I never do it :)***I love Judy's honest post-be honest and tell the mom you guys can hang out or not so it's really low stress :)
To be honest, I sort of roll my eyes at he premise too, BUT, my 5 year old is having no trouble socializing, and if she was, I'd be thinking this over. First of all, this is on the young side for making "real friends". Sure, there are those playdating parents who say their kids have been best friends since age two, but that's not everyone by any means. I see this age group pretty much "Taking or leaving" each other at any given social situation. I dont' remember really having best girlfriends until Jr High-ish. I had classes and stuff, but my parents never scheduled palydates.
My daughter was in K4 last year, and didn't really have a "certain" friend, she just liked everyone and didn't notice the kids who were sort of mean or ignoring her. When I would ask her at home about "who" her friends were, there was no one in particular, or there were different ones each day. She had one kid she stayed after and played in the snow with frequently, but that's just because they were the only two kids allowed to stay and play in the snow for a bit :) When I would ask her if he was her really good friend in class, she didn't even know what I was talking about. Sometimes out in groups of older kids, they'll really be drawn to her, and she's indifferent. I think it takes a couple more years to really get more particular about friends. I'm homeschooling this year, and we meet up with kids for activities, and she'll seem to be bosom buddies for a whole day with someone, and then forget all about them, and play with someone else the next time. Also, in all groups, there are the shyer kids or the not socially skilled ones, but I haven't seen the other kids mind it, and they don't seem unhappy, BUT, that was a Christian K4 and a super nice homeschooling group, so there aren't any cliques or bullies in these scenarios.
Your son has been in so many classes, and you're obviously so on top of this, and so is his teacher, I would not worry so much, personally. Not every kid is meant to be a social butterfly, especially at age 5. My dad was very intelligent, very solitary as a kid, and still only has a "few" good friends instead of lots. If your son is nice, and not acting out, in time he will find a friend or two to relate to, OR he'll suddenly be social in second grade, who knows. The chances of you picking the "right kid" for him to bond with in playdates is iffy. But if you do go that route, try to pick a kid who fits the mold from one of his classes and see if their mom has time to meet etc. I think it would help if he was going to encounter that child in a group, otherwise, he'll still be awkward in a group if his buddy isn't there. No harm, but no point either-except I guess that he'll get used to playing with someone. Just remember, "playdates" are sort of an American thing. Lots of cultures believe socializing is secondary to (or WAY below) learning and wouldn't waste their time on the playdates or give it another thought. So I think if you keep supporting him and he's doing activities and going to school (that's LOTS of socializing, I get tired thinking about it), just do your best and try not to worry.
And yes, WAIT until way after holidays. I would freak out if anyone approached me about anything during January even, we have so much "after Holiday" stuff to start, new classes and stuff. Good luck and good work! And don't take it personally if the first people you ask don't bite the bait, I would NOT have time to meet for a playdate with anyone right now due to younger sibs and schedules, etc, so leave emotions at the door and just ask a couple of people. I like the idea of meeting on neutral turf for a set window of time so it doesn't linger into hours...
Oh, and OFTEN, my daughter will approach groups of kids at the park and be ignored or squeezed out. Luckily, it hasn't made her sad (but it has me), so to an extent, it's normal to have to get squeezed out by kids in this age groups. It stinks when it's your kid.