I honestly have no idea, nor does anyone else, what will be in the crate 50. I'm assuming it will be a salvaged crate, and it will probably follow the previous pattern, 2 useless stranges, and 3 good stranges.
People are massively overstating the value of crate 40's also, they aren't worth more than 10 keys at the moment, they aren't EVEN DISCONTINUED YET! (Sorry for that, it was necessary). The price will surely rise when they are discontinued, but there were a lot more crate 40s dropped than crate 30s I'd expect, due to a larger amount of people playing TF2.
By the looks of it, the salvageds will rotate bi-annually, so we can be expecting the 50 pretty soon. I just hope that, as you say, it isn't a halloween gimmick.

If it is going to be a salvaged I think it is going to be some popular waepons like the spy-cicle and a pomson or anything like that. Then also some relly bad stranges like (I don't kknow relly) the mantreads (that was in the crate #40). They maybe even do a halloween crate as said before but I don't think that they are going to do a crate that is revoved after a while since they did the fall crate notlong ago

I've got a couple ideas for crate #50. Here's my first guess- The crate 50 will be released during the Halloween update. However, it will not be a Halloween crate, that's just the release date. It'll drop at about 1/4 of the rate that salvaged crates do, and look something like this: http://wiki.teamfortress.com/wiki/File:Crate_special_large.png
It'll have some great weapons that everyone likes, MAYBE a crap weapon, maybe. But it'll also have the small (~8%) chance to drop a new, special kind of weapon. What this will be, I don't know. But it would be awesome.
My other idea is pretty much the same, but with a 1/10 drop rate compared to salvaged crates, and instead of having a ~8% chance to drop a special weapon, it'll have a 100% chance to drop it. The weapon will be for any random class, and act like a reverse strange- it'll start at 1,000 kills, and deduct a kill for each kill you get with the weapon. The first 1,000 people to get to kill #0 will receive a special item (a hat, misc, whatever the prize would be). I think either of these ideas would be awesome, but either way, I can't wait for crate #50 to come out :3

Very interesting responses so far. Champelliot, I completely agree about Crate 40. Even though I own a strange or two from it, I agree it and its stranges are becoming way too overpriced way too fast considering the level of abundance.
Big Momma, even more interesting idea. That crate image is bound to spring a bunch of rumors.
SvampsonSWE, you bring up a good point about the Fall Crate, but don't forget, this is Valve we're talking about. They're not above pulling stupid gimmicks for the holidays. (Even though we have more fun with them then we care to admit.) But you may end up being right and it will probably be another salvaged crate.
Lets see if anyone else has opinions on Crate 50.

Strange Original, I really want that in crate 50.

Yeah I'd love a strange original and disciplinary action, spycicle would be great too.

Those would be really good for a salvage crate. Maybe a Strange Shahansha and a Strange Winger too?

Big Momma you got a point there...... They maybe even relese some of the new weapons from workshop in strange quality or even the first weapon in haunted quality (expect the hhhh). Who know as said before it't valve we are talking about!

One thing for sure is that they are going to release some new workshop thing as the "night of the living update" but will they put them in a crate or just in the store or just put it out for drop???

I really hope they won't make another expiring crate, there have been too many lately (Scorched, Fall crate). 50 should be special though since it's kind of a milestone. I expect it to be an extra rare salvaged crate with golden chains like the picture above.

Originally posted by SvampssonSWE(Collecting sydneys):

Big Momma you got a point there...... They maybe even relese some of the new weapons from workshop in strange quality or even the first weapon in haunted quality (expect the hhhh). Who know as said before it't valve we are talking about!

One thing for sure is that they are going to release some new workshop thing as the "night of the living update" but will they put them in a crate or just in the store or just put it out for drop???

HHHH is Unusual.

Originally posted by PS acvdenya (Now On Youtube):

Strange Original, I really want that in crate 50.

They generally don't make strange qualities of reskins. It would be great tho.

Originally posted by PS acvdenya (Now On Youtube):

Strange Original, I really want that in crate 50.

Smokehaze: They generally don't make strange qualities of reskins. It would be great tho. [/quote]

Botkillers. Holy Mackeral (technically a reskin), Rainblower, Lollichop, Festives...Seems like a whole heck of a lot of strange reskins.

Originally posted by 42oSmokeHaze | sleeeep.:

Originally posted by SvampssonSWE(Collecting sydneys):

Big Momma you got a point there...... They maybe even relese some of the new weapons from workshop in strange quality or even the first weapon in haunted quality (expect the hhhh). Who know as said before it't valve we are talking about!

One thing for sure is that they are going to release some new workshop thing as the "night of the living update" but will they put them in a crate or just in the store or just put it out for drop???

HHHH is Uusual

Oh right I forgot that thanks

Strange tape recorder, strange hats, unusual weapons, haunted weapons nuff said

I believe that crate 50 will come soon with S Original and others

Originally posted by DARKJAKE:

Strange tape recorder, strange hats, unusual weapons, haunted weapons nuff said

I don't think that they will add a strange red tepe since they added it to the game not long ago