I have quite a few of the first gen singles and triples and have never had an issue at all. Usually just left a mag in them for a few days to 'break them in' and it was GTG.

Thought I'd give the new stackable version a try because even if I wasn't going to stack them, the option towards modularity/scalability is nice.

I've had a mag in two of them for 3-4 days now, and I can't get the damn mag out unless I use 2 hands. Like there's retention, and then there's 'Im pulling my carrier straight up while pulling up on my magazine, and the magazine barely moves'. This is with slick USGI mags, I could only imagine how hard getting a Lancer or PMAG out of this thing would be.

I know they changed/improved them a bit, but am I missing something, or got an early one with an issue or what?

Anyone else tried this yet?

I've no experience with the stackable Ten Speed, but have you contacted Blue Force? Their CS is on top of things.

Emailed the same day I posted this. No reply.

In the meantime, I've left the mag in the pouches as well as the handle end of a screwdriver and they are loosening a bit, but holy shit.

Suggest you pursue their CS in the meantime, and see what they say.  Post their suggestions here, please.

Might have been made a little tight.  Production tolerances and all. I suggest leaving the pouch in direct sunlight to warm things up a bit, which might help the material to loosen-up some.  Flip it over now and then to equalize the exposure to the sun.  Place the pouch on a black, cloth background.  I would try to insulate the elastic as much as possible, even if only wrapping the elastic in aluminum foil.  Heat destroys elastic, and it's the too-small pouch that's your problem, not the elastic.   Allow the pouch to cool, and re-check your progress often.

This procedure could possibly damage a plastic magazine, or cause it to get soft, thus negating your efforts.  Metal mags, which you mention, are not likely to be damaged.  If desired, a wooden substitute for the mag can be made, but ensure it mimics your intended mag vey closely in shape and size.  Solid plastic training mags might be an alternative, and can prove useful for training.

Might be possible to use a heat gun to do this, but be careful, and avoid heating up any elastic.  This procedure runs the risk of damaging the pouch, if too much heat applied.  Also runs the risk of making the pouch too loose, if the technique works.  In any event, runs the risk of voiding the warranty, so be cautious, and don't over-do it.  Allow the pouch to cool, and re-check your progress often.