I basically want CT access to LootTable.generateLootForPools. Is this out of scope for this mod?

Another improvement related to this is the backport of the /loot function to test our modified loot tables

It would allow more flexibility in dealing with loot tables, allowing creation, modification and utilisation

I basically want CT access to LootTable.generateLootForPools. Is this out of scope for this mod?

Shouldn't be particularly difficult. CraftTweaker already does most of the heavy lifting, which is nice.

Another improvement related to this is the backport of the /loot function to test our modified loot tables

There's already /ct loottables generate, though it works by spawning a chest or entity rather than rolling the loot table directly.
It's a simpler approach to implement correctly and to understand for the end user. /loot is a somewhat complicated command, and I suspect hard to implement correctly. Also hard to make understandable to very new LootTweaker users.

I didn’t know about /ct loottables generate. That helps a lot. It could be useful mentioning it in the docs. Generating a chest is fine for testing. I assuned it would have been easy with generateLootForPools

It could be useful mentioning it in the docs. Generating a chest is fine for testing

It is mentioned in the docs. The page I linked is entirely about /ct loottables.

I assumed it would have been easy with generateLootForPools

The complexity is in specifying the loot context in text form, writing robust parsing for the command, and documenting the use of it. The documentation is the hardest part. The more complex a feature's user-facing part is, the harder it is to document it in a generally understandable way.