More importantly.... do you have a (recent) source for SE saying they would consider releasing this game?

It would make zero sense to do that. Lots of people wanted this to be done around when the game came out (for good reason, most FF players didn't have the type of access to-- or the justification to pay for-- the online play that FFXI was offering at the time) but now? FFXIV is really popular and doing well, FFXI is very aged and definitely does not appeal to many people anymore.

For someone like me, I miss it and I preferred FFXI way over FFXIV (remind me to tell you my depressing FFXIV story sometime...) but I'm a classic FF gal. I like the job systems and the earthy, oaky, shiny appeal that Final Fantasy XI delivered and it felt like only passionate Final Fantasy players wanted to take the time to learn the somewhat obscure features of XI, which I liked...

I just can't see them wanting to spend any time at all reprogramming this game to somehow be single player. The efficiency of a game dev company, especially a large Japanese one like Square Enix, relies on perfectly structured division of work and projects with very small/non-existent margins for time consuming side projects such as this one. But hey, show me a source and I'll read...