Regarding your questions please see my comments below.
Does the RT102x and RT105x SAI-1 I2S running with 4 data lines allow input (or output) at 192Khz sample-rate (with 32bit samples)?
Yes, both RT families (RT102x and RT105x) are capable of working at this sample-rate.
Datasheet seems to suggest yes in the timing diagrams, however the SDK does not have 192K enumerated in library only up to 96Khz... is there a reason why this is limited enum?
Within the SDK we put the most commonly used sample-rates. If a customer wants to work with a different sample-rate they will have to implement this.
Of course we can extend the SW but perhaps there is a reason why? Or a limit related to performance that is not documented?
You can add this sample-rate, as mentioned in my previous answer this is not related to any limitation of the SAI module on the RT.
We are looking to run the FIFO's for all data lines at the full sample rate and also utilize the FIFO's to load into DMA when at threshold - is there any issue to perform this function?
No, you can implement this functionality without problems.