At least in a US context, the proximity advantage is often less about line losses than about the political realities of building transmission. We have way less transmission in the US than we're expected to need as we electrify, and the right-of-way acquisition, permitting, etc., to build new high-voltage transmission are really daunting. NIMBYs tend to hate it (somewhat understandably -- it's ugly), and every jurisdiction along the path of the proposed new line typically has its own permitting process which effectively grants it veto power (unlike gas pipelines, interestingly, where the federal government has permitting authority that supersedes local authority).

A big potential advantage of these kinds of solutions is that you can just site the plant such that you can avoid building the transmission at all. Of course, nuclear obviously has its own NIMBY concerns, permitting issues, etc., so it's not a panacea.