The problem with the Playstation 2 is the COPY PROTECTION system it uses:
DNAS (Dynamic Network Authentication System) is designed to prevent copying of contents from a drive to another and to keep a installed piece of contents from working in a different PS2 console. It's what forces you to format the HDD if you need to move it from one console to another.
The whole debacle comes from the fact that to enlarge the partition designed for the FFXI game they need to submit an application to SONY for the required new partition size. And apparently SONY is no longer accepting such requests.
So if YOU hack it around and artificially enlarge the partition, it fails DNAS check and you have to format the HDD to install again.
I knew it would fail so I didn't try it myself but I have witnessed others try and end needing to reinstall everything.
SONY already shut down most of the DNAS servers for the PS2. The only few exceptions are POL/FFXI and Nobunaga Online for the PS2, apparently and only because these titles can be played on the PS3 which has back compatibility.
So while I don't see anything big being made for FFXI, I don't feel like they would drop it either.
I don't know but I believe that there might be a slim chance that SE could talk SCEI into allowing them to add another 5 or 10 GB to the FFXI partition size.
In a nutshell it's technically doable, but politically tricky to do so.