Hello, everyone. I am currently working on research related to the Mass Timber basement wall system. However, I am now considering the possibility of using a Mass Timber system for the foundation slab instead. Do any of you have any opinions on this?

Yes !

We have now adopted this approach several times in making framing floors and foundations for small buildings using a sandwich of :-

1 - bare, level & compacted earth (needs to be free draining)
2 - phormisol ground cover membrane (as used by plant nurseries)
3 - paving slabs (ideally 2' x 2' x 2")
4 - pallets (creosoted underneath)
5 - interlinking cross ribs (ideally rot resistant cedar) connecting pallets together
6 - plywood (3/4") covering and screwed down onto pallets.
7 - galvanised wire mesh fixed around the pallet edges to prevent critters taking up residence in the underfloor void.
9 - ideally create a shallow trench around the floor to allow rainwater to drain and any build up of leaves to be regularly raked / swept away

We have photos. Check your PM's.