No, this isn’t about shimmer, although shimmer could be useful due to it literally allowing you to noclip.

1.4.4 introduced the ability to switch between gear loadouts, and there seems to actually be quite a bit of potential there.

pretty useless for speedruns as you would need copies of your armor in order to have the armor for both loadouts, as well as for all your accessories. this feature is mostly for more casual play as you get many accessories and weapons and armor sets like switching between a fighting loadout and a fishing loadout. I can't really think of a situation where this would be useful for speedruns except for a very niche situation where your inventory is so full that you need to put excess accessories in a second loadout

I think I've discovered a way to make easy money in 1.4.4 Special crafting stations They sell for gigantic prices

We've known about this for a long time. If you watch nearly any speedrun that needs money you'll see people selling them. They go for about 2 gold a piece, but aren't typically found in high quantities. They're still a good source of money regardless, 2 gold isn't something to scoff at