> surround the reaction chamber with molten FLiBe or lead-lithium

So manufacturing fusion reactors would use a lot of lithium, which is already in short supply. That would be an interesting complication with the demand of lithium for electric vehicle batteries. Maybe the Li supply situation will be eased by then.

The quantity of lithium required is miniscule, but would require a fair bit of enrichment to eliminate the Li-6. The limiting resource is the inner wall for which no known material other than double the annual world production beryllium is even close to sufficient