(by the way i'm NOT joking, this is an exelent way for both to test Sayaka's cloning limit, as well as to build things more efficiently)
Thinking about it, there's a lot of powers that we aren't abusing enough of.
Like what you've said before, Homura's timestop is definitely one of them. Like, we could use it for all sorts of shenanigans. The only real limit for it is that some things require time to pass for them to work.
And our Grief-constructs can do all sorts of things. Not sure what the limits are exactly, but from what I can tell it's "imagining things into existence." Which means that as long as we generally know how to do something, or have a concept of something, then we can do it. And if we don't then we get nonsense like a hallucinating AI. There's also additional restrictions of the construct and it's products not working outside of our range.
Which means that we probably should test it a bit more for the Hildegrade/DeWitching project (from my memory we haven't actually tried a "dewitch" construct yet. I suspect that it won't work, but it's worth trying). Plus, on the off chance it actually succeeds we *do* have a spare body on hand that we can attach her to. And we can always have the technique-copy girl duplicate anything useful.
If we're looking for generally useful constructs, namely ones that can make us a bunch of $$$, then here's a few ideas (as the Science! list has disappeared, please let me know if we've done any of these):
1) A construct that takes in any item, stores its information, and then makes copies of said item. Preferably it should use materials that you input into it as to use less magic making the material from nothing.
2) A construct that draws in/stores Grief.
3) Get technique-copier (sorry I can never remember her name) to copy a Barrier that we make. Ideally, this will result in us plopping semi-permanent pocket dimensions wherever we want
4) From what I remember, enchantments need to be powered by magic from time to time to remain stable. So a "magic battery" would be good
5) A construct that undos what we just did. This could be very useful if some Science! goes horribly wrong. Imagine an undo button or control-z
To be frank, our Greif-Constructs, especially in combination with technique-copy girl, is a power with utility on par with our soul gem cleansing.
And I'd say that the combo with her may be even more potent- after all, we don't know the precise limits of what we can make. How many physical laws can we violate? Say, a time-travel construct or a delete construct.
Ie This has been established, but we are very overpowered. Whoever thought of Sabrina's Wish all those years ago did a good job.