I'm not at all saying that it wont work, I'm just concerned there are too many factors that could screw the move. Not only an increased workload for Thompson in a new position, it's also a lot of pressure and workload to put on a very inexperienced, and semi-unfit, young player in Leilua, who's skillset may be better utilised as an impact player off the bench.
IMO, Host is in front of Leilua when it comes to edge forward spots, but that's sorta beside the point.
The other interesting point you make is at we 'don't have a natural for that [lock] position'. What is a natural lock? The last few years alone have showed how much variety there is in that position alone. There's those who are considered top locks (Taumololo, Merrin, Parker) who are essentially big-minute high-workload players with a bit more footwork and an offload. But if you look at this years' grand finals locks (Finucane and Gallen) they are basically a third prop, with a focus on defensive work rate and technique (i.e deBelins strengths). And there's been a number of variations of strengths at 13 over the last few years, including the Greg Bird/Glenn Stewart ball-player lock. I dont think there's one fit or 'natural', it depends on the rest of the forwards, and outside of Jack we struggle for high-minute/high-workload middle forwards (since the loss of Cooper and Creagh).
In saying all that, Giboz is right, the issues across our spine (and I'll add, in the coaching box) are those that need to be sorted first and foremost. Our forward pack should be able to handle themselves.